Cycloalkyl ethers and thioethers of dipeptides

ABSTRACT

The following dipeptides possess a high order of sweetness: ##STR1## wherein X=O or S; 
     R is alkyl containing 1-3 carbon atoms; 
     R 1  is cycloalkyl, cycloalkenyl, lower alkyl-substituted cycloalkyl or cycloalkenyl, bicycloalkyl, bicycloalkenyl, tricycloalkyl, cyclic ether, cyclic thioether, cyclic sulfoxides, cyclic sulfones, aryl, benzyl, alkylaryl, aromatic heterocyclic or alkyl substituted aromatic heterocyclic containing up to 10 ring carbon atoms and up to a total of 12 carbon atoms; 
     R 2 , R 3 , R 4  and R 6  are each H or lower alkyl; 
     R 5  is H, lower alkyl or cycloalkyl containing 3-5 ring carbons; 
     each n=0, 1 or 2; 
     m=0 or 1; 
     Z is an alkylene chain containing 0-2 carbon atoms in the principal chain and up to a total of 6 carbon atoms; 
     and food-acceptable salts.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a novel group of compounds and more particularto a novel group of compounds particularly well suited as sweeteners inedible foodstuff.

2. Description of the Prior Art

Sweetness is one of the primary taste cravings of both animals andhumans. Thus, the utilization of sweetening agents in foods in order tosatisfy this sensory desire is well established.

Naturally occurring carbohydrate sweeteners such as sucrose, are stillthe most widely used sweetening agents. While these naturally occurringcarbohydrates, i.e., sugars, generally fulfill the requirements of sweettaste, the abundant usage thereof does not occur without deleteriousconsequence, e.g., high caloric intake and nutritional imbalance. Infact, oftentimes the level of these sweeteners required in foodstuffs isfar greater than the level of the sweetener that is desired foreconomic, dietetic or other functional consideration.

In an attempt to eliminate the disadvantages concomitant with naturalsweeteners, considerable research and expense have been devoted to theproduction of artificial sweeteners, such as for example, saccharin,cyclamate, dihydrochalcone, aspartame, etc. While some of theseartificial sweeteners satisfy the requirements of sweet taste withoutcaloric input, and have met with considerable commercial success, theyare not, however, without their own inherent disadvantages. For example,many of these artificial sweeteners have the disadvantages of high cost,as well as delay in the perception of the sweet taste, persistentlingering of the sweet taste, and a very objectionable bitter, metallicaftertaste when used in food products.

Since it is believed that many disadvantages of artificial sweeteners,particularly aftertaste, is a function of the concentration of thesweetener, it has been previously suggested that these effects could bereduced or eliminated by combining artificial sweeteners such assaccharin, with other ingredients such as aspartame or natural sugars,such as sorbitol, dextrose, maltose etc. These combined products,however, have not been entirely satisfactory either. Some U.S. Patentswhich disclose sweetener mixtures include for example, U.S. Pat. Nos.4,228,198; 4,158,068; 4,154,862; and 3,717,477.

Accordingly, much work has continued in an attempt to develop andidentify compounds that have a sweet taste and which will satisfy theneed for better lower calorie sweeteners. Search continues forsweeteners that have intense sweetness, that is, deliver a sweet tasteat low use levels and which will also produce enough sweetness at lowlevels to act as sole sweetener in all or most sweetener applications.Furthermore, the sweeteners sought must have good temporal and sensoryqualities. Sweeteners with good temporal qualities produce atime-intensity sweetness responses similar to natural sweeteners withoutlingering. Sweeteners with good sensory qualities lack undesirable offtastes and aftertaste. Furthermore, these compounds must be economicaland safe to use.

In U.S. Pat. No. 3,798,204 L-aspartyl-O-t-butyl-L-serine methyl esterand L-aspartyl-O-t-amyl-L-serine methyl ester are described as sweetcompounds. These compounds, however, are not entirely satisfactory inproducing a sweet response at low levels of sweetener.

In U.S. Pat. No. 4,448,716 metal complex salts of dipeptide sweetnersare disclosed. In the background of this patent a generic formula isdescribed as an attempt to represent dipeptide sweeteners disclosed infive prior patents: U.S. Pat. Nos. 3,475,403; 3,492,131; Republic ofSouth Africa Patent No. 695,083 published July 10, 1969; Republic ofSouth Africa Patent No. 695,910 published Aug. 14, 1969; and German Pat.No. 2,054,554. The general formula attempting to represent these patentsis as follows: ##STR2##

Wherein R represents the lower alkyls, lower alkyaryls and cycloalkyls,n stands for integers 0 through 5, R₁ represents (a) phenyl group, (b)lower alkyls, (c) cyclo-alkyls, (d) R₂.

Where R₂ is hydroxy, lower alkoxy, lower alkyl, halogen, (e)(S(O)_(m)(lower alkyl) where m is 0, 1 or 2 and provided n is 1 or 2, (f) R₃.

Where R₃ represents an hydroxy or alkoxy and (g) single or doubleunsaturated cycloalkyls with up to eight carbons. These compounds alsoare not entirely satisfactory in producing a high quality sweetness orin producing a sweet response at low levels of sweetener.

Dipeptides of aspartyl-cysteine and aspartyl-methionine methyl estersare disclosed by Brussel, Peer and Van der Heijden in Chemical Sensesand Flavour, 4, 141-152 (1979) and in Z. Lebensm. Untersuch-Forsch.,159, 337-343 (1975). The authors disclose the following dipeptides:

α-L-Asp-L-Cys(Me)-OMe

α-L-Asp-L-Cys(Et)-OMe

α-L-Asp-L-Cys(Pr)-OMe

α-L-Asp-L-Cys(i-Pr)-OMe

α-L-Asp-L-Cyst(t-But)-OMe

α-L-Asp-L-Met-OMe

European Patent Application No. 34,876 describes amides of L-aspartyl-D-amino acid dipeptides of the formula: ##STR3## wherein R^(a) is methyl,ethyl, n-propyl or isopropyl and R is a branched aliphatic, alicylic orheterocyclic member which is branched at the alpha carbon atom and alsobranched again at one or both of the beta carbon atoms. These compoundsare indicated to be of significant sweetness.

Despite the past efforts in this area, research continues. Accordingly,it is desired to find compounds that provide quality sweetness whenadded to foodstuffs or pharmaceuticals at low levels and thus eliminateor greatly diminish disadvantages associated with prior art sweeteners.

SUMMARY OF THE INVENTION

The present new compounds are dipeptides of certain α-aminodicarboxylicacids and etherified hydroxy α-amino-mono-carboxylic acid esters whichare low calorie sweeteners that possess a high order of sweetness, withpleasing taste and little, if any, aftertaste.

This invention provides new sweetening compounds represented by theformula: ##STR4## wherein X=O or S;

R is alkyl containing 1-3 carbon atoms;

R₁ is cycloalkyl, cycloalkenyl, lower alkyl-substituted cycloalkyl orcycloalkenyl, bicycloalkyl, bicycloalkenyl, tricycloalkyl, cyclic ether,cyclic thioether, cyclic sulfoxides, cyclic sulfones, aryl, benzyl,alkylaryl, aromatic heterocyclic or alkyl substituted aromaticheterocyclic containing up to 10 ring carbon atoms and up to a total of12 carbon atoms;

R₂, R₃, R₄ and R₆ are each H or lower alkyl;

R₅ is H, lower alkyl or cycloalkyl containing 3-5 ring carbons;

each n=0, 1 or 2;

m=0 or 1;

Z is an alkylene chain containing 0-2 carbon atoms in the principalchain and up to a total of 6 carbon atoms;

and food-acceptable salts.

Compounds of the above formula have a surprisingly high order ofsweetness and pleasant taste and are particularly suitable for lowercalorie sweetening of foods and pharmaceuticals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, the preferred novel compoundsof the invention are represented by the formula: ##STR5## wherein m=0 or1, and each n, Z and R₁ -R₆ has the same meaning as in formula I.

Additional stereoisomers in the present new compound exist in thosecompounds wherein R₄ is not identical to R₃. Mixtures of these isomersare, of course, useful as sweeteners and are desired. The mixtures maybe resolved into the corresponding D and L forms.

Especially preferred compounds of the formula ##STR6## wherein R₁ and R₃are as previously defined. These compounds are readily preparable andshow the highest levels of sweetness.

The alpha aminodicarboxylic acids of the present new dipeptides areaspartic acid and aminomalonic acid, of which aspartic acid ispreferred. The etherified mercapto and hydroxy alpha-aminomonocarboxylicacids are etherified serine, threonine and cysteine, and homologsthereof such as beta-hydroxy alpha-aminovaleric acid, gamma-hydroxyalpha-aminobutyric acid, gamma-hydroxy alpha-aminovaleric acid,beta-hydroxy alpha-aminobutyric acid, beta-mercapto alpha-aminovalericacid, gamma-mercapto alpha-aminobutyric acid and similar such aminoacids and lower alkyl esters. The ether group in these acids is a cyclichydrocarbyl group comprising cycloalkyl, cycloalkenyl, bicycloalkyl,tricycloalkyl, bicycloalkenyl, cyclic ether, cyclic thioether, cyclicsulfoxides, cyclic sulfones, aryl, aralkyl, or a cyclic ether orthioether. The ether group is directly attached to the ether oxygen orsulfur, or separated by an alkylene chain from the ether oxygen orsulfur.

In accordance with the present sweetener taste testing, the preferredcompounds are those in which the aminodicarboxylic acid group isα-aspartyl and the aminomonocarboxylic acid ester is cysteine, threonineor serine methyl ester, and of these, serine and cysteine methyl estersare preferred.

The ether groups of the present new compounds includes such groups ascycloalkyl, e.g., cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl,etc.; alkyl-substituted cycloalkyls, e.g., 1-methylcyclopentyl,1-methylcyclohexyl, 1-methylcyclobutyl, 1-methylcycloheptyl,1-ethylcyclobutyl, 1-ethylcyclopentyl, 1-ethylcycloheptyl,1-ethylcyclohexyl, 1-isopropylcyclobutyl, 1-isopropylcyclopentyl,1-isopropylcyclohexyl, 1-isopropylcycloheptyl, 1,2-dimethylcyclohexyl,1,2-dimethylcyclopentyl, 1,2-dimethylcycloheptyl,1,3-dimethylcyclohexyl, 1,3-dimethylcyclopentyl,1,3-dimethylcycloheptyl, 1,4-dimethylcyclohexyl,1,4-dimethylcycloheptyl, 2,3-dimethylcyclopentyl,2,3-dimethylcyclohexyl, 2,3-dimethylcycloheptyl,2,4-dimethylcyclopentyl, 2,4-dimethylcyclohexyl,2,4-dimethylcycloheptyl, 2,5-dimethylcyclopentyl,2,5-dimethylcyclohexyl, 2,5-dimethylcycloheptyl, 2,6-dimethylcyclohexyl,2,6-dimethylcycloheptyl, 2,7-dimethylcycloheptyl,3,4-dimethylcyclopentyl, 3,4-dimethylcyclohexyl,3,4-dimethylcycloheptyl, 3,5-dimethylcyclohexyl,3,5-dimethylcycloheptyl, 4,5-dimethylcycloheptyl,3,6-dimethylcyclohexyl, 3,6-dimethylcycloheptyl,4,6-dimethylcycloheptyl, 5,6-dimethylcyclohexyl,2,2-dimethylcyclopentyl, 2,2-dimethylcyclohexyl,2,2-dimethylcycloheptyl, 3,3-dimethylcyclopentyl,3,3-dimethylcyclohexyl, 3,3-dimethylcycloheptyl, 4,4-dimethylcyclohexyl,4,4-dimethylcycloheptyl, 2,2,3-trimethylcyclopentyl,2,2,3-trimethylcyclohexyl, 2,2,3-trimethylcycloheptyl,2,2,4-trimethylcyclopentyl, 2,2,4-trimethylcyclohexyl,2,2,4-trimethylcycloheptyl, 2,2,5-trimethylcyclopentyl,2,2,5-trimethylcyclohexyl, 2,2,5-trimethylcycloheptyl,2,2,6-trimethylcyclohexyl, 2,2,6-trimethylcycloheptyl,2,2,7-trimethylcycloheptyl, 1,2,2-trimethylcyclopentyl,1,2,2-trimethylcyclohexyl, 1,2,2-trimethylcycloheptyl,1,3,3-trimethylcyclopentyl, 1,3,3-trimethylcyclohexyl,1,3,3-trimethylcycloheptyl, 1,4,4-trimethylcyclohexyl,1,4,4-trimethylcyclopentyl, 3,3,4-trimethylcyclopentyl,3,3,4-trimethylcyclohexyl, 3,3,4-trimethylcycloheptyl,2,3,3-trimethylcyclopentyl, 2,3,3-trimethylcyclohexyl,2,3,3-trimethylcycloheptyl, 2,4,4-trimethylcyclopentyl,2,4,4-trimethylcyclohexyl, 2,4,4-trimethylcycloheptyl,1,2,3-trimethylcyclopentyl, 1,2,3-trimethylcyclohexyl,1,2,3-trimethylcycloheptyl, 1,2,4-trimethylcyclopentyl,1,2,4-trimethylcyclohexyl, 1,2,4-trimethylcycloheptyl,1,2,5-trimethylcyclopentyl, 1,2,5-trimethylcyclohexyl,1,2,5-trimethylcycloheptyl, 1,2,6-trimethylcyclohexyl,1,2,6-trimethylcycloheptyl, 1,2,7-trimethylcycloheptyl,2,3,4-trimethylcyclopentyl, 2,3,4-trimethylcyclohexyl,2,3,4-trimethylcycloheptyl, 2,3,5-trimethylcyclopentyl,2,3,5-trimethylcyclohexyl, 2,3,5-trimethylcycloheptyl,2,3,6-trimethylcyclohexyl, 2,3,6-trimethylcycloheptyl,2,3,7-trimethylcycloheptyl, 3,4,4-trimethylcyclohexyl, 3,4,4-trimethyl,2,2,5,5-tetramethylcyclopentyl, 2,2,5,5-tetramethylcyclohexyl,2,2,5,5-tetramethylcycloheptyl, 2,2,6,6-tetramethylcyclohexyl,2,2,6,6-tetramethylcycloheptyl, 2,2,7,7-tetramethylcycloheptyl,2,2,4,4-tetramethylcyclopentyl, 2,2,4,4-tetramethylcyclohexyl,2,2,4,4-tetramethylcycloheptyl, 2,2,3,3-tetramethylcyclopentyl,2,2,3,3-tetramethylcyclohexyl, 2,2,3,3-tetramethylcycloheptyl,3,3,4,4-tetramethylcyclopentyl, 3,3,4,4-tetramethylcyclohexyl,3,3,4,4-tetramethylcycloheptyl, 3,3,5,5-tetramethylcyclohexyl,3,3,5,5-tetramethylcycloheptyl, 1,2,3,4-tetramethylcyclopentyl,1,2,3,4-tetramethylcyclohexyl, 1,2,3,4-tetramethylcycloheptyl,1,2,3,5-tetramethylcyclopentyl, 1,2,3,5-tetramethylcyclohexyl,1,2,3,5-tetramethylcycloheptyl, 1,2,3,6-tetramethylcyclohexyl,1,2,3,6-tetramethylcycloheptyl, 2,3,4,5-tetramethylcyclopentyl,2,3,4,5-tetramethylcyclohexyl, 2,3,4,5-tetramethylcycloheptyl,2,3,4,6-tetramethylcycloheptyl, 2,3,4,6-tetramethylcyclohexyl,2,3,4,7-tetramethylcycloheptyl, 2,2,3,4-tetramethylcyclopentyl,2,2,3,4-tetramethylcyclohexyl, 2,2,3,4-tetramethylcycloheptyl,2,2,3,5-tetramethylcyclopentyl, 2,2,3,5-tetramethylcyclohexyl,2,2,3,5-tetramethylcycloheptyl, 2,2,3,6-tetramethylcyclohexyl,2,2,3,6-tetramethylcycloheptyl, 2,2,3,7-tetramethylcycloheptyl,2,3,3,4-tetramethylcyclohexyl, 2,3,3,4-tetramethylcyclopentyl,2,3,3,4-tetramethylcycloheptyl, 2,3,3,5-tetramethylcyclopentyl,2,2,3,5-tetramethylcyclohexyl, 2,3,3,5-tetramethylcycloheptyl,2,3,3,6-tetramethylcyclohexyl, 2,3,3,6-tetramethylcycloheptyl,2,3,3,7-tetramethylcycloheptyl, 2,2,3,4-tetramethylcyclopentyl,2,2,3,4-tetramethylcyclohexyl, 2,3,3,4-tetramethylcycloheptyl,2,2,3,5-tetramethylcyclopentyl, 2,2,3,5-tetramethylcyclohexyl,2,2,3,6-tetramethylcyclohexyl, 2,2,3,6-tetramethylcycloheptyl,2,2,3,7-tetramethylcycloheptyl, 2,2,4,5-tetramethylcyclopentyl,2,2,4,5-tetramethylcyclohexyl, 2,2,4,5-tetramethylcycloheptyl,2,2,4,6-tetramethylcyclohexyl, 2,2,4,6-tetramethylcycloheptyl,2,2,4,7-tetramethylcycloheptyl, 4-methylcyclohexylisopropyl,4-methylcycloheptylisopropyl, 3-methylcyclopentylisopropyl,3-methylcyclohexylisopropyl, 3-methylcycloheptylisopropyl,2-methylcycloheptylisopropyl, 2-methylcyclohexylisopropyl,2-methylcyclopentylisopropyl, dicyclopropylmethyl,t-butylcyclopropylmethyl, t-butylcyclopentylmethyl,2-isopropylcyclopentyl, 2-t-butylcyclopentyl, 2-isopropylcyclohexyl,2-t-butylcyclopentyl, 2-isopropylcyclohexyl, 2-t-butylcyclohexyl,2-t-amylcyclopentyl, t-amylcyclopropylmethyl, dicyclobutylmethyl,t-butylcyclobutylmethyl, etc., cycloalkenes, e.g., cyclopentenyl,cyclohexenyl, cycloheptenyl, etc.; alkyl-substituted cycloalkenes, e.g.,1-methyl-3-cyclopentenyl, 1-methyl-3-cyclohexenyl,1-methyl-3-cycloheptenyl, 1-methyl-4-cycloheptenyl,3-cyclopentenylisopropyl, 3-cyclohexenylisopropyl,3-cycloheptenylisopropyl, 4-cycloheptenylisopropyl,3-cyclopentenylmethyl, 3-cyclopentenylethyl, 3-cyclohexenylpropyl,3-cyclohexenylethyl, 3-cycloheptenylpropyl, 3-cycloheptenylethyl,4-cycloheptenylmethyl, 4-cycloheptenylethyl, 2-methyl-3-cyclohexenyl,2-methyl-3-cyclopentenyl, 2-methyl-3-cycloheptenyl,2-methyl-4-cycloheptenyl, 3-methyl-3-cyclohexenyl,3-methyl-3-cyclopentenyl, 3-methyl-3-cycloheptenyl,4-methyl-3-cycloheptenyl, 4-methyl-3-cyclohexenyl,4-methyl-3-cyclopentenyl, 5-methyl-3-cyclopentenyl,5-methyl-3-cyclohexenyl, 5-methyl-3-cycloheptenyl,6-methyl-3-cyclohexenyl, 6-methyl-3-cycloheptenyl,2-methyl-2-cyclopentenyl, 2-methyl-2-cyclohexenyl,2-methyl-2-cycloheptenyl, 2-methyl-2-cyclopentenyl,3-methyl-2-cyclohexenyl, 3-methyl-2-cycloheptenyl,1-methyl-2-cyclopentenyl, 1-methyl-2-cyclohexenyl,1-methyl-2-cycloheptenyl, 5-methyl-2-cyclohexenyl,4-methyl-2-cyclopentenyl, 4-methyl-2-cycloheptenyl,5-methyl-2-cyclohexenyl, 5-methyl-2-cycloheptenyl,6-methyl-2-cyclohexenyl, 6-methyl-2-cycloheptenyl,7-methyl-2-cycloheptenyl, 2,3-dimethyl- 2-cyclopentenyl,2,3-dimethyl-2-cyclohexenyl, 2,4-dimethyl-2-cyclopentenyl,2,4-dimethyl-2-cyclohexenyl, 2,5-dimethyl-2-cyclohexenyl, 2,5-dimethyl-2-cycloheptenyl, 2,6-dimethyl-2-cyclohexenyl,2,6-dimethyl-3-cyclohexenyl, 2,5-dimethyl-3-cyclohexenyl,2,5-dimethyl-2-cyclopentenyl, 2,4-dimethyl-3-cyclopentenyl,2,4-dimethyl-3-cyclohexenyl, 3,3-dimethyl-3-cyclopentenyl,3,3-dimethyl-3-cyclohexenyl, 3,4-dimethyl-3-cyclopentenyl,3,4-dimethyl-3-cyclohexenyl, 4,5-dimethylcyclo-3-pentenyl,4,5-dimethyl-3-cyclo-3-hexenyl, 5,5-dimethyl-3-cyclohexenyl,5,5-dimethylcyclopentenyl, 5,5-dimethylcyclohexenyl,6,6-dimethylcyclohexenyl, 1,2-dimethyl-3-cyclopentenyl,1,2-dimethyl-3-cyclohexenyl, 1,3-dimethyl-3-cyclopentenyl,1,3-dimethyl-3-cyclohexenyl, 1,3-dimethyl-3-cycloheptenyl,1,4-dimethyl-3-cyclopentenyl, 1,4-dimethyl-3-cyclohexenyl,1,4-dimethyl-3-cyclohexenyl, 1,5-dimethyl-3-cyclopentenyl,1,5-dimethyl-3-cyclohexenyl, 1,5-dimethyl-3-cycloheptenyl,2,2,6-trimethyl-3-cyclohexenyl, 2,2,5-trimethyl-3-cyclohexenyl,2,5,5-trimethyl-3-cyclohexenyl, 2,5,5-trimethyl-3-cyclopentenyl,2,7,7-trimethyl-3-cycloheptenyl, 2,7,7-trimethyl-4-cycloheptenyl,2,2,7-trimethyl-3-cycloheptenyl, 2,2,7-trimethyl-4-cycloheptenyl,2,3,6-trimethyl-3-cyclohexenyl, 2,3,7-trimethyl-3-cycloheptenyl,2,3,5-trimethyl-3-cyclopentenyl, 2,2,6,6-tetramethyl-3-cyclohexenyl,2,2,5,5-tetramethyl-3-cyclopentenyl,2,2,7,7-tetramethyl-3-cycloheptenyl,2,3,5,5-tetramethyl-3-cyclopentenyl, 2,3,6,6-tetramethyl-3-cyclohexenyl,2,3,7,7-tetramethyl-3-cycloheptenyl,2,3,6,6-tetramethyl-3-cycloheptenyl, 2,3,5,5-tetramethyl-3-cyclohexenyl,2,3,4,5-tetramethyl-3-cyclopentenyl, 2,3,4,5-tetramethyl-3-cyclohexenyl,(4-ethylcyclohex-3-enyl)isopropyl, (4-propylcyclohex-3-enyl)isopropyl,(4-methylcyclohex-3-enyl)ethyl, (3-methylcyclohex- 3-enyl)isopropyl,(4-ethylcyclopent-3-enyl)isopropyl, (4-propylcyclopent-3-enyl)isopropyl,(4-methylcyclopent-3-enyl)isopropyl, (4-methylcyclopent-3-enyl)ethyl,(3-methylcyclopent-3-enyl)isopropyl, (2-methylcyclohex-3-enyl)isopropyl,(2-methylcyclopent-3-enyl)isopropyl, etc.; bicyclic compounds, such asnorbornyl, norcaranyl, norpinanyl, bicyclo [2.2.2] octyl, etc.; alkylsubstituted bicyclic compounds, e.g., 6,6-dimethyl bicyclo [3.1.1]heptyl, 6,7,7-trimethylnorbornyl (bornyl), pinanyl, thujanyl, caranyl,fenchyl, 2-norbornylmethyl, 2-norbornylethyl, 2-norbornylpropyl,3-norbornylpropyl, etc.; unsubstituted and alkyl-substitutedbicycloalkenes such as norborenyl, norpinenyl, norcarenyl,2-(4-norborenyl)ethyl, pinenyl, carenyl, fenchenyl, etc.,tricyclocompounds such as adamantyl and alkyl-substituted adamantyl,etc., and cyclic ethers, such as 2,3-dihydrofuryl, 2,3-dihydropyranyl,3,4-dihydropyranyl, tetrahydrofuryl, tetrahydropyranyl; alkylsubstituted cyclic ethers, such as 3-(2,2-dimethyltetrahydrofuryl),3-(4,4-dimethyltetrahydrofuryl), 3-(2,3-dimethyltetrahydrofuryl),3-(2,4-dimethyltetrahydrofuryl), 3-(2,5-dimethyltetrahydrofuryl),3-(3,4-dimethyltetrahydrofuryl), 3-(3,5-dimethyltetrahydrofuryl),3-(4,5-dimethyltetrahydrofuryl), 2-(3,3-dimethyltetrahydrofuryl),2-(4,4-dimethyltetrahydrofuryl), 2-(5,5-dimethyltetrahydrofuryl),2-(2,3-dimethyltetrahydrofuryl), 2-(2,4-dimethyltetrahydrofuryl),2-(2,5-dimethyltetrahydrofuryl), 2-(3,4-dimethyltetrahydrofuryl),2-(3,5-dimethyltetrahydrofuryl), 2-(4,5-dimethyltetrahydrofuryl),3-(2,2,3-trimethyltetrahydrofuryl), 3-(2,2,4-trimethyltetrahydrofuryl),3-(2,2,5-trimethyltetrahydrofuryl), 3-(2,3,4-trimethyltetrahydrofuryl,3-(2,3,5-trimethyltetrahydrofuryl), 3-(2,4,5-trimethyltetrahydrofuryl),3-(2,5,5-trimethyltetrahydrofuryl), 3-(3,4,4-trimethyltetrahydrofuryl,3-(3,5,5-trimethyltetrahydrofuryl), 3-(4,5,5 -trimethyltetrahydrofuryl),3-(2,2,5,5-tetramethylhydrofuryl), 2-(2,2,4,4-tetramethylhydrofuryl),3-(2,3,4,5-tetramethylhydrofuryl), 3-(2,4,5,5-tetramethylhydrofuryl),3-(2,3,5,5-tetramethylhydrofuryl), 2-(2,3,3-trimethyltetrahydrofuryl),2-(2,3,4-trimethyltetrahydrofuryl), 2-(2,3,5-trimethyltetrahydrofuryl),2-(2,4,5-trimethyltetrahydrofuryl), 2-(2,5,5-trimethyltetrahydrofuryl),2-(3,3,4-trimethyltetrahydrofuryl), 2-(3,3,5-trimethyltetrahydrofuryl),2-(3,4,5-trimethyltetrahydrofuryl), 2-(4,4,5-trimethyltetrahydrofuryl),2-(2,3,3,4-tetramethylhydrofuryl), 2-(2,3,3,5-tetramethylhydrofuryl),2-(2,3,4,5-tetramethylhydrofuryl), 2-(2,3,5,5-tetramethylhydrofuryl),2-(2,3,4,4-tetramethylhydrofuryl), 2-(2,3,5,5-tetramethylhydrofuryl),2-(3,3,4,5-tetramethylhydrofuryl), 2-(3,3,5,5-tetramethylhydrofuryl),2-(3,4,5,5-tetramethylhydrofuryl), 2-(2,3,4,5-tetramethylhydrofuryl),2-(4,4,5,5-tetramethylhydrofuryl), 3-furylmethyl, 2-furylmethyl,2-(5-methylfuryl)methyl, and the corresponding furfuryl compounds, andthe corresponding tetrahydropyranyls, as well as the corresponding2,3-dihydrofuryl, 2,3-dihydropyranyl, 3,4-dihydropyranyl, as well as thecorresponding cyclic thioethers, such as 2-thienylmethyl,3-thienylmethyl, 2-(5-methylthienyl)methyl, etc., and the correspondingcyclic sulfones or cyclic sulfoxides thereof; aryl or alkylaryl, such asphenyl, 2,6-dimethylphenyl, 2,5-dimethylphenyl, 2,4-dimethylphenyl,2,3-dimethylphenyl, 3,4-dimethylphenyl, 3,5-dimethylphenyl,3,6-dimethylphenyl, 2,3,4-trimethylphenyl, benzyl, α-methylbenzyl,o-methylbenzyl, etc.

The preferred R₁ is cycloalkyl or alkyl-substituted cycloalkyl,especially where the alkyl group is in the α, β, or β' positions.Further preferred groups include alkyl-substituted furyl, thienyl,dihydro- and tetrahydrofuryl, phenyl and o-and m-alkylphenyl. Furtherpreference exists for compounds in which R₁ is a cycloalkyl with one,two, three, or four alkyl groups in the β,β' positions such asβ,β,β',β'-tetraalkyl-substituted cyclopentyl, cyclohexyl, andcycloheptyl, as well as β,β,β'-trialkyl substituted andβ,β,β'-trisubstituted-cyclohexyl, cyclopentyl, and cycloheptyl.

Illustrated preferred compounds include.

α-L-aspartyl-O-(1-methylcyclobutyl)-L-serine methyl ester

α-L-aspartyl-O-cyclopentyl-L-serine methyl ester

α-L-aspartyl-O-(1-methylcyclopentyl)-L-serine methyl ester

α-L-aspartyl-O-(1-ethylcyclopentyl)-L-serine methyl ester

α-L-aspartyl-O-(1-propylcyclopentyl)-L-serine methyl ester

α-L-aspartyl-O-(1-isopropylcyclopentyl)-L-serine methyl ester

α-L-aspartyl-O-(1,2-dimethylcyclopentyl)-L-serine methyl ester

α-L-aspartyl-O-(1,2,5-trimethylcyclopentyl)-L-serine methyl ester

α-L-aspartyl-O-(1,2,2-trimethylcyclopentyl)-L-serine methyl ester

α-L-aspartyl-O-(2,2,5,5-tetramethylcyclopentyl)-L-serine methyl ester

α-L-aspartyl-O-cyclohexyl-L-serine methyl ester

α-L-aspartyl-O-(1-methylcyclohexyl)-L-serine methyl ester

α-L-aspartyl-O-(1-ethylcyclohexyl)-L-serine methyl ester

α-L-aspartyl-O-(1-propylcyclohexyl)-L-serine methyl ester

α-L-aspartyl-O-(1-isopropylcyclohexyl)-L-serine methyl ester

α-L-aspartyl-O-(1,2-dimethylcyclohexyl)-L-serine methyl ester

α-L-aspartyl-O-(1,2,6-trimethylcyclohexyl)-L-serine methyl ester

α-L-aspartyl-O-(1,2,2-trimethylcyclohexyl)-L-serine methyl ester

α-L-aspartyl-O-(2,2,6,6-tetramethylcyclohexyl)-L-serine methyl ester

α-L-aspartyl-O-cycloheptyl-L-serine methyl ester

α-L-aspartyl-O-(1-methylcycloheptyl)-L-serine methyl ester

α-L-aspartyl-O-(1-ethylcycloheptyl)-L-serine methyl ester

α-L-aspartyl-O-(1-propylcycloheptyl)-L-serine methyl ester

α-L-aspartyl-O-(1-isopropylcycloheptyl)-L-serine methyl ester

α-L-aspartyl-O-(1,2-dimethylcycloheptyl)-L-serine methyl ester

α-L-aspartyl-O-(1,2,7-trimethylcycloheptyl)-L-serine methyl ester

α-L-aspartyl-O-(1,2,2-trimethylcyclohelptyl)-L-serine methyl ester

α-L-aspartyl-O-(2,2,7,7-tetramethylcycloheptyl)-L-serine methyl ester

α-L-aspartyl-[O-(3-methylcyclohexyl)]-L-serine methyl ester

α-L-aspartyl-[O-(3-methylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(1-methylcyclopentyl)]-L-threonine methyl ester

α-L-aspartyl-[O-2,2,5,5-tetramethylcyclopentyl]-L-serine methyl ester

α-L-aspartyl-O-(2,2,6,6-tetramethylcyclohexyl-L-serine methyl ester

α-L-aspartyl-O-(1,2,7-trimethylcycloheptyl)-L-serine methyl ester

α-L-aspartyl-O-(1,2,2-trimethylcycloheptyl)-L-serine methyl ester

α-L-aspartyl-O-(2,2,7,7-tetramethylcycloheptyl)-L-serine methyl ester

α-L-aspartyl-[O-(2,2,5-trimethylcyclopentyl]-L-serine methyl ester

α-L-aspartyl-[O-(2,2-dimethylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2,5-dimethylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2,6-dimethylcyclohexyl)]-L-serine methyl ester

α-L-aspartyl-[O-2,2,6-trimethylcyclohexyl]-L-serine methyl ester

α-L-aspartyl-S-(1-ethylcyclobutyl)-L-cysteine methyl ester

α-L-aspartyl-S-cyclopentyl-L-cysteine methyl ester

α-L-aspartyl-S-(1-methylcyclopentyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1-ethylcyclopentyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1-propylcyclopentyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1-isopropylcyclopentyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1,2-dimethylcyclopentyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1,2,5-trimethylcyclopentyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1,2,2-trimethylcyclopentyl)-L-cysteine methyl ester

α-L-aspartyl-S-(2,2,5,5-tetramethylcyclopentyl)-L-cysteine methyl ester

α-L-aspartyl-S-cyclohexyl-L-cysteine methyl ester

α-L-aspartyl-S-(1-methylcyclohexyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1-ethylcyclohexyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1-propylcyclohexyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1-isopropylcyclohexyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1,2-dimethylcyclohexyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1,2,6-trimethylcyclohexyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1,2,2-trimethylcyclohexyl)-L-cysteine methyl ester

α-L-aspartyl-S-(2,2,6,6-tetramethylcyclohexyl)-L-cysteine methyl ester

α-L-aspartyl-S-cycloheptyl-L-cysteine methyl ester

α-L-aspartyl-[O-(2,2-dimethylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2,2-dimethylcyclohexyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2,2,4,4-tetramethylcyclobutyl)-L-serine methyl ester

α-L-aspartyl-[O-(2-methylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-methylcyclohexyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-isopropylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-isopropylcyclohexyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-t-butylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-t-butylcyclohexyl)]-L-serine methyl ester

α-L-aspartyl-[O-(dicyclopropylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(dicyclobutylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(t-butylcyclopropylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(t-butylcyclobutylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(fenchyl)]-L-serine methyl ester

α-L-aspartyl-[O-(benzyl)]-L-serine methyl ester

α-L-aspartyl-[O-(α-methylbenzyl)]-L-serine methyl ester

α-L-aspartyl-[O-(o-methylbenzyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-furylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(3-furylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-2-(5-methylfuryl)methyl]-L-serine methyl ester

α-L-aspartyl-[O-(2-thienylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(3-thienylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-2-(5-methylthienyl)methyl]-L-serine methyl ester

α-L-aspartyl-S-(1-methylcycloheptyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1-ethylcycloheptyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1-propylcycloheptyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1-isopropylcycloheptyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1,2-dimethylcycloheptyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1,2,7-trimethylcycloheptyl)-L-cysteine methyl ester

α-L-aspartyl-S-(1,2,2-trimethylcyclohelptyl)-L-cysteine methyl ester

α-L-aspartyl-S-(2,2,7,7-tetramethylcycloheptyl)-L-cysteine methyl ester

α-L-aspartyl-[S-(3-methylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(3-methylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,2,5,5-tetramethylcyclopentyl)]-L-cysteine methylester

α-L-aspartyl-[S-(2,2,6,6-tetramethylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(1,2,7-trimethylcycloheptyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(1,2,2-trimethylcycloheptyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,2,7,7-tetramethylcycloheptyl)]-L-cysteine methylester

α-L-aspartyl-[S-(2,2,5-trimethylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,2-dimethylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,5-dimethylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,6-dimethylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,2,6-trimethylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,2-dimethylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,2-dimethylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,2,4,4-tetramethylcyclobutyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-methylcylopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-methylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-isopropylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-isopropylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-t-butylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-t-butylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(dicyclopropylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(dicyclobutylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(t-butylcyclopropylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(t-butylcyclobutylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(fenchyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(benzyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(α-methylbenzyl)]-L-cysteine nethyl ester

α-L-aspartyl-[S-(o-methylbenzyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-furylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(3-furylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-2-(5-methylfuryl)methyl]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-thienylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(3-thienylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-2-(5-methylthienyl)methyl]-L-cysteine methyl ester

Furthermore, when the sweetness agents of the present invention areadded to ingesta, the sweetness agents may be added alone or withnontoxic carriers such as the abovementioned sweeteners or other foodingredients such as acidulants and natural and artificial gums. Typicalfoodstuffs, and pharmaceutical preparations, in which the sweetnessagents of the present invention may be used are, fcr example, beveragesincluding soft drinks, carbonated beverages, ready to mix beverages andthe like, infused foods (e.g. vegetables or fruits), sauces, condiments,salad dressings, juices, syrups, desserts, including puddings, gelatinand frozen desserts, like ice creams, sherbets, icings and flavoredfrozen desserts on sticks, confections, toothpaste, mouthwash, chewinggum, cereals, baked goods, interrmediate moisture foods (e.g. dog food)and the like.

In order to achieve the effects of the present invention, the compoundsdescribed herein are generally added to the food product at a levelwhich is effective to perceive sweetness in the food stuff and suitablyis in an amount in the range of from about 0.0005 to 2% by weight basedon the consumed product. Greater amounts are operable but not practical.Preferred amounts are in the range of from about 0.001 to about 1% ofthe foodstuff. Generally, the sweetening effect provided by the presentcompounds is experienced over a wide pH range, e.g. 2 to 10 preferably 3to 7 and in buffered and unbuffered formulations.

It is desired that when the sweetness agents of this invention areemployed alone or in combination with another sweetener, the sweeteneror combination of sweeteners provide a sucrose equivalent in the rangeof from about 2 weight percent to about 40 weight percent and morepreferably from about 3 weight percent to about 15 weight percent in thefoodstuff or pharmaceutical.

A taste procedure for determination of sweetness merely involves thedetermination of sucrose equivalency. Sucrose equivalence for sweetenersare readily determined. The amount of a sweetener that is equivalent toa given weight percent sucrose can be determined by having a panel oftasters taste solutions of a sweetener at known concentrations and matchits sweetness to standard solutions of sucrose.

In order to prepare compounds of the present invention several reactionschemes may be employed. In one reaction scheme compounds of the generalformulas II (protected α-aminodicarboxylic acid) and III (protectedetherified hydroxy or mercapto amino acid alkyl ester are condensed toform compounds of the general formula IV (protectedL-aminodicarboxyl-O-cycloalkyl-L-hydroxyamino acid alkyl ester ethers orthe protected L-aminodicarboxyl-S-cycloalkyl-L-mercaptoamino alkyl esterethers). Susequent removal of protecting groups A and B from compoundsof general formula Iv give the desired compounds of general formula I.##STR7##

In these, group A is an amino protecting group, B is a carboxylprotecting group and R, R₁, R₂, R₃, R₄, R₅, R₆, Z, X, m and n have thesame meaning as previously described. A variety of protecting groupsknown in the art may be employed. Examples of many of these possiblegroups may be found in "Protective Groups in Organic Synthesis" by T. W.Green, John Wiley and Sons, 1981. Among the preferred groups that may beemployed are benzyloxycarbonyl for A and benzyl for B.

Coupling of compounds with general formula II to compounds havinggeneral formula III employs established techniques in peptide chemistry.One such technique uses dicyclohexylcarbodiimide (DCC) as the couplingagent. The DCC method may be employed with or without additives such as4-dimethylaminopyridine or copper (II). The DCC coupling reactiongenerally proceeds at room temperature, however, it may be carried outfrom about -20° to 50° C. in a varrety of solvents inert to thereactants. Thus suitable solvents include, but are not limited to,N,N-dimethyl-formamide, methylene chloride, toluene and the like.Preferably the reaction is carried out under an inert atmosphere such asargon or nitrogen. Coupling usually is complete within 2 hours but maytake as long as 24 hours depending on reactants

Various other methods can be employed to prepare the desired compounds.The following illustrates such methods using aspartic acid as the aminodicarboxylic acid and serine as the amino monocarboxylic acid. Ofcourse, other amino di- and monocarboxylic acids can be substituted forthese exemplary acids.

For example, U.S. Pat. Nos. 3,786,039; 3,833,553; 3,879,372 and3,933,781 disclose the reaction of N-protected aspartic anhydrides withamino acids and amino acid derivatives to yield the desired products.These N-protected aspartic anhydrides can be reacted with compounds offormula III by methods disclosed in the above patents. As described inU.S. Pat. No. 3,786,039 compounds of formula III can be reacted directlyin inert organic solvents with L-aspartic anhydride having its aminogroup protected by a formyl, carbobenzloxy, or p-methoxycarbobenzloxygroup which is subsequently removed after coupling to give compounds ofgeneral formula I. The N-acyl-L-aspartic anhydrides are prepared byreacting the corresponding acids with acetic anhydride in amounts of1.0-1.2 moles per mole of the N-acyl-L-aspartic acid at 0° to 60° C. inan inert solvent. The N-acyl-L-aspartic anhydrides are reacted withpreferably 1 to 2 moles of compounds of formula III in an organicsolvent capable of dissolving both and inert to the same. Suitablesolvents are, but not limited to, ethyl acetate, methyl propionate,tetrahydrofuran, dioxane, ethyl ether, N,N-dimethylformamide andbenzene. The reaction proceeds smoothly at 0° to 30° C. The N-acyl groupis removed after coupling by catalytic hydrogenation with palladium oncarbon or with HBr or HCl in a conventional manner. U.S. Pat. No.3,879,372 discloses that this coupling method can also be performed inan aqueous solvent at a temperature of -10° to 50° C. and at a pH of4-12.

Another method for the synthesis of the desired compounds is thereaction of compounds of formula III with suitable aspartic acidderivatives in which protecting groups have been attached to the aminoand beta-carboxy groups and the alpha carboxy group has been convertedto a reactive ester function. As disclosed in U.S. Pat. No. 3,475,403these coupled products may be deprotected as described to yield thedesired compounds of formula I.

An alternative scheme to the desired coupled compounds involves reactionof compounds of formula III with L-aspartic acid N-thiocarboxyanhydrideby the method of Vinick and Jung, Tet. Lett., 23, 1315-18 (1982). Anadditional coupling method is described by T. Miyazawa, Tet. Lett., 25,771 (1984).

Compounds of general formula III may be synthesized from N-protectedserine methyl ester by employing a variety of etherification methodsknown in the art. Some of these methods may be found in "ModernSynthetic Reactions", 2nd ed., by H. O. House, W. A. Benjamin Inc.,1972; "Advanced Organic Chemistry," 2nd ed., by J. March, McGraw-Hill,1977, and "Compendium of Organic Synthetic Methods," Vol. 1 and 2, by I.T. Harrison & S. Harrison, Wiley-Interscience, 1971 & 1974.

One possible etherification method is the acid catalyzed reaction ofN-protected serine methyl ester with an appropriate olefinic precursorof the desired R₁ moiety. For example, when N-carbobenzyloxy-L-serine isreacted with methylene cyclopentane the N-protected intermediate ofgeneral formula III where R₁ represents 1-methyl cyclopentane isobtained. This intermediate is then deprotected to give a compound offormula III having R₁ equal to 1-methyl cyclopentane. Whencycloalkadienes are used, the product is a cycloalkenyl ether. Asillustrative examples, the following R₁ olefinic precursors can beutilized to give the corresponding saturated R₁ group:

    ______________________________________     R.sub.1 Precursor  R.sub.1 Group    ______________________________________    methylenecyclobutane                       1-methylcyclobutyl    1-methyl-1-cyclobutene                       1-methylcyclobutyl    1-methyl-1-cyclopentene                       1-methylcyclopentyl    1-methyl-1-cyclohexene                       1-methylcyclohexyl    methylenecyclohexane                       1-methylcyclohexyl    1,2-dimethyl-1-cyclohexene                       1,2-dimethylcyclohexyl    1-methyl-1-cycloheptene                       1-methylcycloheptyl    1-ethyl-1-cyclohexene                       1-ethylcyclohexyl    1-ethyl-1-cyclopentene                       1-ethylcyclopentyl    1,3-cyclopentadiene                       2-cyclopentenyl    1-methyl-1,4-cyclohexadiene                       1-methyl-1-cyclohex-3-enyl    d-limonene         (1,1-dimethyl)-1-(4-methyl-                       cyclohex-3-enyl)-methyl    ______________________________________

The reaction of an appropriate olefinic R₁ precursor with N-protectedserine methyl ester is preferably carried out in the presence of an acidcatalyst. Any acid is employable but a mineral acid such as sulfuricacid is advantageous. Usually an excess of from 1.2 to 50 moles of theolefin precursor is utilized. Reaction temperatures are in the range of-10° to 40° C. and reaction times range from 2 to 48 hours. The reactionis carried out in a solvent that will dissolve both reactants and isinert to both as well. Solvents include, but are not limited to,methylene chloride, toluene, tetrahydrofuran, chloroform and the like.Usually an inert atmosphere of nitrogen or argon is supplied.

Another possible etherification method is the base, or other catalyst,promoted reaction of N-protected serine methyl ester with an R₁ X, whereX is an organic leaving group such as halide, tosylate or mesylate. Anybase normally employed to deprotonate an alcohol may be used, such assodium hydride, sodium hydroxide, triethylamine, or diisopropylethylamine. Reaction temperatures are in the range of -78° to 100° C.and reaction times vary from 2 to 48 hours. The reaction is carried outin a solvent that will dissolve both reactants and is inert to both aswell. Solvents include, but are not limited to, diethyl ether,tetrahydrofuran, N,N-dimethylformamide, dimethylsulfoxide, and the like.Usually an inert atmosphere of nitrogen or argon is supplied.

Alternatively, a neutral catalyst such as mercury (II) salts or nickel(II) 2,4-pentanedionate may be employed in this reaction. Thesereactions are also carried out in inert solvents at room temperature orabove. The intermediate formed in this reaction is deprotected to yieldcompounds of formula III.

A third method is the solvomercuration-demercuration reaction of theappropriate olefinic precursor of R₁ with N-protected serine methylester. The reaction of the olefin with N-protected serine methyl esterin the presence of mercuric acetate or mercury trifluoroacetate iscarried out at a reaction temperature of -10° to 100° C. in a solventwhich will dissolve both reactants and is inert to both. Solventsinclude, but are not limited to, diethyl ether, tetrahydrofuran,methylene chloride, and the like. Reaction times vary from 5 minutes to24 hours. The resulting organomercury intermediate is reduced in situwith basic aqueous sodium borohydride, or other reducing agents, toremove the mercury, followed by deprotection to yield compounds ofgeneral formula III.

A fourth method of etherification is the reaction of N-protectedbeta-X-L-alanine methyl ester, where X is halide, tosylate, mesylate orother leaving group, with R₁ OH using a base or other catalyst. Any basenormally employed to deprotonate an alcohol may be used, includingsodium hydride, sodium hydroxide, triethylamine, or diisopropylethylamine. The reaction may be run either with or without additives,for example, copper salts. Reaction temperatures are in the range of-78° C. to 100° C., and reaction times vary from 2 to 48 hours. Thereaction is carried out in a solvent that will dissolve both reactantsand is inert to both. Solvents include, but are not limited to, diethylether, tetrahydrofuran, N,N-dimethylformamide, dimethylsulfoxide, andthe like. Usually an inert atmosphere of nitrogen or argon is supplied.

Alternatively, a neutral catalyst such as mercury (II) salts or nickel(II) 2,4-pentanedionate may be employed in this reaction. These are alsocarried out in inert solvents at room temperature or above. This productis then deprotected to yield compounds of general formula III.

To prepare compounds in which R₂ and R₃ are alkyl, the starting compoundshould have a corresponding side chain with a double bond within thecorresponding side chain, as exemplified by limonene, in which the sidechain is ##STR8## in which case 1,2 addition occurs on the side chainand does not involve ring carbon atoms.

With regard to the removal of protecting groups from compounds offormula IV and N-protected precursors of formula III, a number ofdeprotecting techniques are known in the art and can be utilized toadvantage depending on the nature of the protecting groups. Among suchtechniques is catalytic hydrogenation utilizing palladium on carbon ortransfer hydrogenation with 1,4-cyclohexadiene. Generally the reactionis carried at room temperature but may be conducted from 5° to 65° C.Usually the reaction is carried out in the presence of a suitablesolvent which may include, but are not limited to water, methanol,ethanol, dioxane, tetrahydrofuran, acetic acid, t-butyl alcohol,isopropanol or mixtures thereof The reaction is usually run at apositive hydrogen pressure of 50 psi but can be conducted over the rangeof 20 to 250 psi. Reactions are generally quantitative taking 1 to 24hours for completion.

In any of the previous synthetic methods the desired products arepreferably recovered from reaction mixtures by crystallization.Alternatively, normal or reverse-phase chromatography may be utilized aswell as liquid/liquid extraction or other means.

The desired compounds of formula I are usually obtained in the free acidform; they may also be recovered as their physiologically acceptablesalts, i.e., the corresponding amino salts such as hydrochloride,sulfate, hydrosulfate, nitrate, hydrobromide, hydroiodide, phosphate orhydrophosphate; or the alkali metal salts such as the sodium, potassium,lithium, or the alkaline earth metal salts such as calcium or magnesium,as well as aluminum, zinc and like salts.

Conversion of the free peptide derivatives of formula I into theirphysiologically acceptable salts is carried out by conventional means,as for cxample, bringing the compounds of formula I into contact with amineral acid, an alkali metal hydroxide, an alkali metal oxide orcarbonate or an alkaline earth metal hydroxide, oxide, carbonate orother complexed form.

These physiologically acceptable salts can also be utilized as sweetnessagents usually having increased solubility and stability over their freeforms.

The following examples further illustrate the invention.

EXAMPLE I Preparation of L-aspartyl-O-(1-methylcyclopentyl)-L-serinemethyl ester A. N-Carbenzyloxy (CBZ)-L-serine methyl ester.

N-CBZ-L-serine (25 g) was dissolved in 100 ml of dry N,N-dimethylformamide at 0° C. under argon. Triethylamine (2 e.g., 30 ml)and dimethylsulfate (20 ml) were added. The contents of the vessel werestirred overnight at room temperature and then poured into 500 ml ofwater and extracted with ethyl acetate (3×200 ml). The organic layer waswashed with water and brine and dried with sodium sulfate. Rotaryevaporation afforded an oil which crystallized after silica gelchromatography in pure ethyl ether. The structure of the product,N-CBZ-L-serine methyl ester, was confirmed by NMR spectroscopy.

B. N-CBZ-O-(1-methylcyclopentyl)-L-serine methylester.

N-CBZ-L-serine methyl ester (3.15 g) was dissolved in 40 ml ofdichloromethane at 0° C. under argon. Methylenecyclopentane (20 ml) wasadded, followed by 16 drops of concentrated sulfuric acid. The contentsof the vessel were stirred at room temperature overnight then pouredinto dilute aqueous sodium hydrogen carbonate and extracted withchloroform (2×30 ml). The organic layer was dried over sodium sulfateand evaporated. The residual oil was chromatographed on silica gel with50/50 petroleum ether/diethyl ether to give an oil (78% yield). Theproduct, N-CBZ-O-(1-methylcyclopentyl)-L-serine methyl ester, wasconfirmed by NMR spectroscopy.

C. O-1-methylcyclopentyl-L-serine methyl ester.

In a Paar hydrogenation bottle N-CBZ-O-(1 -methylcyclopentyl)-L-serinemethyl ester (2.7 g) was dissolved in methanol (50 ml) and purged withargon. Palladium on carbon (5%) (290 mg) was added and hydrogenationcarried out at 50 psi. After cessation of hydrogen uptake the contentsof the bottle were filtered through Celite and evaporated to give 1.65 g(93% yield) of the product.

D. N-CBZ-beta-benzyl-alpha-L-aspartyl-O-(1-methylcyclopentyl)-L-serinemethyl ester.

O-(1-methylcyclopentyl)-L-serine methyl ester (1.65 g) was dissolved inN, N-dimethylformamide (96 ml) at 0° C. under argon.N-CBZ-alpha-L-aspartic acid-beta-benzyl ester (2.87 g) was added,followed by copper (II) chloride (1.08 g). Finally,dicyclohexylcarbodiimide (1.66 g) was added. The contents of the flaskwere stirred at room temperature over three hours and then poured intowater (500 ml) and acidified to pH 5 with 2N hydrochloric acid. Theproduct was extracted with (2×400 ml) ethyl acetate and dried oversodium sulfate. Rotary evaporation afforded an oil which waschromatographed on silicagel with 2:1 petroleum ether/ethyl acetate togive an oil (3.4 g) (77% yield). The productN-CBZ-beta-benzyl-L-aspartyl-O-(l-methylcyclopentyl)-L-serine methylester was confirmed by mass spectrometry and NMR spectroscopy.

E. L-aspartyl-O-(1-methylcyclopentyl)-L-serine methyl ester.

To a Paar hydrogenation bottle the N-CBZ-beta-benzyl ester protectedpeptide (2.5 g) was dissolved in absolute methanol (120 ml) and purgedwith argon. Palladium on carbon (5%) (300 mg) was added andhydrogenation carried out at 50 psi. After cessation of hydrogen uptakethe contents of the bottle were filtered through Celite and evaporatedto give a white solid (1.45 g) (99% yield).

Reverse phase chromatography on C₁₈ silica with 50% methanolic watergave pure L-aspartyl-O-(1-methylcyclopentyl)-L-serine methyl ester.Structure was confirmed by NMR spectroscopy and mass spectrometry.

The following sensory evaluations were obtained by a panel of expertsusing known weight percent aqueous solutions of the above compoundmatched to sucrose standard solutions as previously described.

    ______________________________________    Concentration Sucrose Equivalent    ______________________________________    0.005%        2.5%    0.010%         5%    0.025%        10%    0.05%         12%    ______________________________________

It was further determined by the panel of experts that the sweetenerpossessed excellent temporal and sensory qualities.

EXAMPLE 2 L-aspartyl-O-(l-methylcyclohexyl)-L-serine methyl ester

This compound was prepared in an identical manner as disclosed inExample 1 except 1-methyl-1-cyclohexene was substituted for methylenecyclopentane.

The following sensory evaluations were obtained by a panel of expertsusing known weight percent aqueous solutions of the above compoundmatched to sucrose standard solutions as previously described.

    ______________________________________    Concentration Sucrose Equivalent    ______________________________________    0.005%        2%    0.010%        4.5%    0.025%        8.5%    ______________________________________

EXAMPLE 3 L-aspartyl-O-(l-methylcyclobutyl)-L-serine methyl ester.

This compound was prepared in an identical manner as described inExample 1 except methylenecyclobutane was substituted for methylenecyclopentane.

The following sensory evaluations were obtained by a panel of expertsusing known weight percent aqueous solutions of the above compoundmatched to sucrose standard solutions as previously described.

    ______________________________________    Concentration Sucrose Equivalent    ______________________________________    0.01%         2%    0.05%         8%    ______________________________________

EXAMPLE 4 L-aspartyl-O-(cis-l,2-dimethylcyclohexyl)-L-serine methylester and L-aspartyl-O-(trans-1,2-dimethylcyclohexyl)-L-serine methylester.

These compounds were prepared in an identical manner as described inExample 1 except 1,2-dimethyl-1-cyclohexene was substituted formethylenecyclopentane. The cis and trans isomers were separated afteretherification by HPLC on silica using 6:1 hexane: ethyl acetate,carried through to end products, and evaluated separately.

The following sensory evaluations were obtained by a panel of expertsusing known weight percent aqueous solutions of the above compoundsmatched to sucrose standard solutions as previously described.

    ______________________________________    Concentration Sucrose Equivalent    ______________________________________    CIS ISOMER    0.005%        2.0%    0.010%        4.0%    0.020%        7.0%    TRANS ISOMER    0.005%        1.5%    0.010%        3.0%    0.020%        5.0%    ______________________________________

EXAMPLE 5 L-aspartyl-O-(1-ethylcyclopentyl)-L-serine methyl ester.

This compound was prepared in an identical manner as described inExample 1 except 1-ethyl-1-cyclopentene was substituted formethylenecyclopentane.

The following sensory evaluations were obtained as described.

    ______________________________________    Concentration Sucrose Equivalent    ______________________________________     0.005%       2%    0.01%         4%    0.02%         6%    ______________________________________

EXAMPLE 6 Preparation ofα-L-aspartyl-O-(1-methylcyclopentyl)-L-threonine methyl ester A.N-Carbenzyloxy(CBZ)-O-(1-methylcyclopentyl)-L-threonine methyl ester

N-CBZ-L-threonine methyl ester is etherified with 1-methylcyclopenteneby using the same sulfuric acid catalyzed procedure as described inExample 1B, to afford the product.

B. N-CBZ-β-benzyl ester-α-L-aspartyl-O-(1-methylcyclopentyl)-L-threoninemethyl ester

O-(1-methylcyclopentyl)-L-threonine methyl ester (prepared by catalytichydrogenation of N-CBZ-O-(1-methylcyclopentyl)-L-threonine methyl ester,as described in Example 1, C.), N-CBZ-alpha-L-aspartic acid-beta benzylester and N,N-dimethylformamide are added to a dry flask under argon at0° C. Copper (II) chloride was next added. After the dissolution of thesalt, dicyclohexylcarbodiimide is added. The contents of the flask arestirred at room temperature for 16 hours and poured into water (300 ml)and 0.1 N hydrochloric acid (100 ml). The product is extracted withdiethyl ether (3×100 ml) and is dried over sodium sulfate. Rotaryevaporation affords an oil which is chromatographed over silica gel with3:1 petroleum ether/ethyl acetate to give an oil of the diastereomericproducts.

C. α-L-aspartyl-O-(1-methylcyclopentyl)-L-threonine methyl ester

The product from B is catalytically hydrogenated as described in Example1E to afford the product.

EXAMPLE 7 Preparation of L-aspartyl-O-(1-methylcyclohex-3-enyl)-L-serinemethyl ester A. N-CBZ-O-(1-methylcyclohex-3-enyl)-L-serine methyl ester

This compound is prepared in an identical manner as disclosed in Example1B, except 1-methyl-1,4-cyclohexadiene is substituted for methylenecyclopentane. The product is characterized by NMR spectroscopy.

B. O-1-methylcyclohex-3-enyl-L-serine methyl ester

The amino olefin was prepared by utilizing transfer hydrogenation ratherthan catalytic hydrogenation. TheN-CBZ-O-(1-methylcyclohex-3-enyl)-L-serine methyl ester (691 mg, 2.2mmol) was dissolved in absolute ethyl alcohol (9 ml) at 0° C. in anultrasound bath. Palladium on carbon (10%) (695 mg) was added. Thehydrogen source, 1,4-cyclohexadiene (2 ml, 20 equiv.) was added andultrasound commenced for eight minutes. The slurry was then filteredthrough a bed of Celite with ethyl alcohol. Rotary evaporation affordsan oil (382 mg, 98% yield) whose NMR spectrum indicates a free amine andcyclohexenyl moiety.

C. N-CBZ-β-benzyl-α-L-aspartyl-O-(1-methylcyclohex-3-enyl) -L-serinemethyl ester

The compound prepared in B above was reacted with N-CBZ-α-L-asparticacid-β-benzyl ester in a manner as previously described in Example 1D,to afford the above product.

D. α-L-aspartyl-O-(1-methylcyclohex-3-enyl)-L-serine methyl ester

The protected dipeptide from the previous step (277 mg, 0.54 mmol) wasdissolved in absolute ethyl alcohol (2 ml), and 10% palladium on carbon(240 mg) was added. The hydrogen source, 1,4-cyclohexadiene (1 ml, 10equiv.), was added, and ultrasound commenced for five minutes. Theslurry was then filtered through a bed of Celite with ethyl alcohol.Rotary evaporation afforded a white solid (158 mg).

EXAMPLE 8 A. N-CBZ-O-(1-(4-methylcyclohex-3-enyl)isopropyl)-L-serinemethyl ester

The ether is prepared from N-CBZ-L-serine methyl ester and α-limonene ina manner similar to that described in Example 1B. The product can becharacterized by NMR spectroscopy.

B. N-CBZ-β-benzylester-α-L-aspartyl-O-(1-(4-methylcyclohex-3-enyl)isopropyl)-L-serinemethyl ester

The amine olefin is prepared by transfer hydrogenation as described inExample 7B and coupled with N-CBZ-α-L-aspartic acid-β-benzyl ester bythe copper mediated procedure as described in Example 1D.

C. α-L-aspartyl-O-(1-(4-methylcyclohex-3-enyl)isopropyl)-L-serine methylester

The protected dipeptide is deprotected by transfer hydrogenation, asdescribed in Example 7B, to giveα-L-aspartyl-O-1-(4-methylcyclohex-3-enyl)isopropyl)-L-serine methylester.

D. α-L-aspartyl-O-(1-(cis-4-methylcyclohexyl)isopropyl)-L-serine methylester

The product of B above is deprotected by catalytic hydrogenation in amanner as described in Example 1E to afford the above compound.

The following sensory evaluations were obtained by a panel of expertsusing known weight percent aqueous solutions of the above compoundmatched to sucrose standard solutions as previously described:

    ______________________________________    Sensory Evaluations    Concentrations                  Sucrose Equivalent    ______________________________________    0.01          2.2    0.025         5.2    ______________________________________

EXAMPLE 9 Preparation of DL-2-aminomalonyl-O-(1-methylcyclopentyl)-L-serine methyl ester A.N-CBZ-DL-2-amino malonic acid mono benzyl ester

Dibenzyl malonate (10.0 g, 35.2 mmol) was taken up in 1,4-dioxane (100mL) and treated with a 40% aqueous solution of acetic acid (35 mL),followed by the slow addition (2.5 h) of solid sodium nitrite (10 g).The reaction was stirred for another 2.5 h and extracted into ether(3×70 mL). The organic phase was washed with a 1% solution of NaHCO₃until the aqueous layer was slightly acidic (pH 5-6). The etherealsolution was dried over MgSO₄ and removed under reduced pressure to givean oil (10.9 g). The crude oxime was carried directly to the next step.

Amalgamated aluminum (obtained from 1.25 g, 0.463 g atom of aluminumfoil) was covered with tetrahydrofuran (28 mL) followed by 1.9 mL ofwater. The reaction mixture was stirred mechanically and cooled in a dryice acetone bath. A solution of the crude oxime (from the previous step)in 30 mL of tetrahydrofuran was added dropwise (20 min.) while thetemperature was maintained between -15° and -30° C. The ice bath wasremoved and spontaneous reaction occurred, which resulted in a rapidrise in temperature (50° C.). When the evolution of heat ceased, themixture was refluxed for 1 hour, diluted with ether (100 mL) andfiltered through Celite. The solvent was removed under reduced pressureto give the crude amine (7.5 g), which was taken to the following stepwithout further purification. The crude amine (7 g) was dissolved in asaturated solution of NaHCO₃ (200 mL) and cooled in an ice bath. Benzylchloroformate (4.0 g, 23 mmol) was added dropwise (0.5 h) to thevigorously stirred solution. The reaction mixture was left at roomtemperature for 12 hours, during which time the product precipitated.The product was collected by filtration, washed with water, dried inair, and recrystallized from i-PrOH: yield 4.8 g (52%) from dibenzylmalonate; m.p. 104°-106° C.

N-(benzyloxycarbonyl)-2-amino malonic acid dibenzyl ester (4.33 g, 10mmol) was dissolved in acetone/water (4.1, 133 mL). The solution wasstirred and lithium hydroxide monohydrate (0.42 g, 10 mmol) in water (11mL) was added dropwise (1 h). The reaction mixture was stirred for 12hours at room temperature, the acetone was removed under reducedpressure, and the residue was taken up into a saturated solution ofNaHCO₃ (60 mL) and extracted with EtOAc (3×100 ml). The EtOAc washingswere combined, dried over MgSO₄ and removed under reduced pressure togive a solid, which was crystallized from EtOAc/hexane. This solid wasidentified as recovered starting material (1.1 g, 25.4%). The aqueousphase was acidified with 3 N HCl to pH=1 and extracted with CHCl₃ (4×50mL). The combined CHCl₃ washings were dried over MgSO₄ and the solventwas removed under reduced pressure to give a residue which crystallizedfrom i-PrOH: yield 2.0 g (58%); m.p. 114°-116° C.

B. N-CBZ-DL-2-amino malonyl benzyl ester-O-1-methylcyclopentyl)-L-serinemethyl ester

The mono carboxylic acid from the last step of Section A (2 g, 5.83mmol) was dissolved in dry acetonitrile (75 ml) at 0° C. under argon.Then, O-(1-methylcyclopentyl) O-L-serine methyl ester, (1.2 g, 1 equiv.)was added, as described in Example 1D. Lastly, dicyclohexylcarbodiimide(1.2 g, 1 equiv.) was added and the contents of the flasks were stirredat room temperature.

The reaction mixture was rotary evaporated to remove the acetonitrileand the residue was taken up in 0.1 N hydrochloric acid (100 ml) andextracted with diethyl ether (3×100 ml). The ethereal layer was driedover sodium sulfate and filtered to remove insoluble urea. The ether isremoved by rotary evaporation. The coupled product was purified bysilica gel chromatography with 3:1 petroleum ether/ethyl acetate.

C. DL-2-amino malonyl-O-(1-methylcyclopentyl)-L-serine methyl ester

The bis-protected dipeptide from Section B was dissolved in absolutemethanol under argon. 10% Palladium on carbon was added andhydrogenation was carried out at 50 psi. After cessation of hydrogenuptake, the mixture was filtered through Celite and rotary evaporated togive a white solid.

EXAMPLE 10 α-L-Aspartyl-O-2,2,5,5-tetramethylcyclopentyl-L-serine methylester A. L-N-Triphenylmethyl serine methyl ester

A solution of L-serine methyl ester hydrochloride (100 g),triphenylmethylchloride (179.3 g) and triethylamine (197 ml) was stirredat 0° C. for 2 hours, then allowed to warm to room temperatureovernight. The solution was then washed successively with 10% aqueouscitric acid and water, dried over magnesium sulfate, and the solvent wasevaporated to yield 212 g of the product (91% yield).

B. L-1-Triphenylmethyl-aziridine-2-carboxylic acid methyl ester

A mixture of compound A (212 g), methanesulfonyl chloride (45.6 ml), andpyridine (1.76 1) was stirred at 0° C., then allowed to warm slowly toroom temperature overnight. Ethyl acetate (1.5 1) was added, and theresulting solution was washed with 10% aqueous citric acid and water,dried over magnesium sulfate and the solvent was removed. The residualoil was dissolved in tetrahydrofuran (2.5 l) and a triethylamine (143ml) was added. The mixture was heated at reflux overnight. The solutionwas then cooled, and most of the solvent was removed under vacuum. Theresidual oil was dissolved in ethyl acetate (2 l) and the solution waswashed succesively with 10% aqueous citric acid, saturated aqueoussodium bicarbonate, and water, was dried over magnesium sulfate, and thesolvent was evaporated under vacuum. The residue was dissolved in hotmethanol (300 ml). Upon cooling, compound B crystallized as an off-whitepowder which was removed by filtration and then air dried (115 g), (57%yield). The structure was confirmed by NMR. [α ]²⁵ _(D) =-90.5° (±0.5)(C 1.0 THF).

C. L-1-Benzyloxycarbonylaziridine-2-carboxylic acid methyl ester

To a cold solution (0° C.) of compound B (17.0 g) and methanol (100 ml)in dichloromethane (100 ml) was added concentrated sulfuric acid (5.0ml). The mixture was stirred at 0° for 10 min. Approximately half of thesolvent was removed under vaccum, and the residue was dissolved inether. This solution was extracted with water. The aqueous extract wasmade basic with sodium bicarbonate are extracted with dichloromethane(3×25 ml). To these combined extracts was added triethylamine (4.63 g)and the solution was cooled to 0°. Benzyl chloroformate (7.80 g), wasadded, and the mixture was allowed to warm to room temperatureovernight. The solution was then washed successively with 1 M aqueoushydrochloric acid and saturated aqueous sodium bicarbonate, dried overmagnesium sulfate, and the solvent was removed under vacuum to yield abrown oil (7.0 g). The product was purified by column chromatography onsilica gel (4:1 hexanes: ethyl acetate, eluent) to yield compound C(3.44 g, 30%) as a slightly yellow oil.

D. N-Benzyloxycarbonyl-O-2,2,5,5-tetramethylcyclopentyl-L-serine methylester

To a solution of compound C (1.00 g) and2,2,5,5-tetramethylcyclopentanol (1.2 g) in dichloromethane (20 ml) wasadded boron trifluoride diethyl etherate (15 drops). The mixture wasstirred at room temperature for 4 hours, then washed with water, driedover magnesium sulfate and the solvent was evaporated. The residue waspurified by column chromatography (silica gel, 10:1, hexanes: ethylacetate, eluent) to yield compound D as a colorless oil (0.34 g, 21%yield).

E. O-2,2,5,5-Tetramethylcyclopentyl-L-serine methyl ester

Compound D (0.34 g) was deprotected by the usual procedure to yieldcompound E (0.214 g, 98% yield).

F. N-Benzyloxycarbonyl-α-L-aspartyl-β-benzylester-O-2,2,5,5-tetramethylcyclopentyl-L-serine methyl ester

Compound E (0.214 g) was coupled with N-benzyloxy carbonyl-L-asparticacid-β-benzyl ester (0.33 g) by the copper (II) chloride procedure toyield compound F (0.300 g, 60% yield).

G. α-L-Aspartyl-O-(2,2,5,5-tetramethylcyclopentyl)-L-serine methyl ester

Compound F (0.300 g) was deprotected by the usual procedure to yieldcompound G (0.090 g, 43% yield).

Using appropriate starting materials in this procedure, the followingcompounds are prepared:

α-L-aspartyl-O-2,2,6,6-tetramethylcyclohexyl-L-serine methyl ester

α-L-aspartyl-O-1,2,7-trimethylcycloheptyl-L-serine methyl ester

α-L-aspartyl-O-1,2,2-trimethylcycloheptyl-L-serine methyl ester

α-L-aspartyl-O-2,2,7,7-tetramethylcycloheptyl-L-serine methyl ester

α-L-aspartyl-[O-(2,2,3,3-tetramethylcyclopropyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2,2,4,4-tetramethylcyclobutyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2,2,5-trimethylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2,5-dimethylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-O-2-methylcyclohexyl-L-serine methyl ester

α-L-aspartyl-O-cyclohexyl-L-serine methyl ester

α-L-aspartyl-O-cyclopentyl-L-serine methyl ester

α-L-aspartyl-O-cyclobutyl-L-serine methyl ester

α-L-aspartyl-O-(2,2,6-trimethylcyclohexyl)-L-serine methyl ester

α-L-aspartyl-O-(2-ethylcyclopentyl)-L-serine methyl ester

α-L-aspartyl-O-(2-isopropylcyclohexyl)-L-serine methyl ester

α-L-aspartyl-O-(2-t-butylcyclopentyl)-L-serine methyl ester

α-L-aspartyl-O-(2,2,6-trimethylnorbornyl)-L-serine methyl ester

α-L-aspartyl-[O-(2,2-dimethhylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2,2-dimethylcyclohexyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2,2,4,4-tetramethylcyclobutyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-methylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-methylcyclohexyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-isopropylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-isopropylcyclohexyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-t-butylcyclopentyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-t-butylcyclohexyl)]-L-serine methyl ester

α-L-aspartyl-[O-(dicyclopropylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(dicyclobutylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(t-butylcyclopropylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(t-butylcyclobutylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(fenchyl)]-L-serine methyl ester

α-L-aspartyl-[O-(benzyl)]-L-serine methyl ester

α-L-aspartyl-[O-(α-methylbenzyl)]-L-serine methyl ester

α-L-aspartyl-[O-(o-methylbenzyl)]-L-serine methyl ester

α-L-aspartyl-[O-(2-furylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(3-furylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-2-(5-methylfuryl)methyl]-L-serine methyl ester

α-L-aspartyl-[O-(2-thienylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-(3-thienylmethyl)]-L-serine methyl ester

α-L-aspartyl-[O-2-(5-methylthienyl)methyl]-L-serine methyl ester

EXAMPLE 11 α-L-Aspartyl-O-1-bornyl-L-serine methyl ester

This compound was prepared in an identical manner as described inExample 1 except camphene was substituted for methylenecyclopentane.

Similarly, α-L-Aspartyl-O-1-norbornyl-L-serine methyl ester andα-L-Aspartyl-O-[2-(4-norbornenyl)ethyl]-L-serine methyl ester wereprepared using norbornene and ethylidenylnorbornene, respectively.

α-L-Aspartyl-O-2-norbornylethyl-L-serine methyl ester was prepared bythe catalytic hydrogenation of-L-Aspartyl-O-[2-(4-norbornenyl)ethyl]-L-serine methyl ester.

EXAMPLE 12 (α-L-aspartyl-O-(1-methyl-cycloheptyl)-L-serine methyl ester

Using the same procedure as disclosed in Example 1 and substituting1-methyl-1-cycloheptene for methylene cyclopentane,α-L-aspartyl-O-(1-methylcycloheptyl)-L-serine methyl ester was prepared.

EXAMPLE 13 α-L-Aspartyl-O-cyclopentyl-L-serine methyl ester

This compound is prepared according to the method as described inExample 10, except cyclopentanol is substituted for2,2,5,5-tetramethylcyclopentanol.

EXAMPLE 14 αL-aspartyl-S-(cis-1,2-dimethylcyclohexyl)-L-cysteine methylester and α-aspartyl-S-(trans-1,2-dimethylcyclohexyl)-L-cysteine methylester

These compounds were prepared in an identical manner as described inExample 14, except 1,2-dimethyl-1-cyclohexene was substituted for1-methyl-1-cyclopentene. The cis and trans isomers were separated afteretherification by HPLC on silica using 6:1 hexane: ethyl acetate,carried through to end products and evaluated separately.

EXAMPLE 15 Preparation ofL-aspartyl-S-(1-methylcyclohex-3-enyl)-L-cysteine methyl ester A.N-CBZ-S-(1-methylcyclohex-3-enyl)-L-cysteine methyl ester

This compound is prepared in an identical manner as disclosed in Example1B, except 1-methyl-1,4-cyclohexadiene is substituted for methylenecyclopentane. The product is characterized by NMR spectroscopy.

B. S-1-methylcyclohex-3-enyl-L-cysteine methyl ester

The amino olefin was prepared by utilizing transfer hydrogenation ratherthan catalytic hydrogenation. TheN-CBZ-S-(1-methylcyclohex-3-enyl)-L-cysteine methyl ester (691 mg, 2.2mmol) was dissolved in absolute ethyl alcohol (9 ml) at 0° C. in anultrasound bath. Palladium on carbon (10%) (695 mg) was added. Thehydrogen source, 1,4-cyclohexadiene (2 ml, 20 equiv.) was added andultrasound commenced for eight minutes. The slurry was then filteredthrough a bed of Celite with ethyl alcohol. Rotary evaporation affordsan oil (382 mg, 98% yield) whose NMR spectrum indicates a free amine andcyclohexenyl moiety.

C. N-CBZ-β-benzyl-β-L-aspartyl-S-(1-methylcyclohex-3-enyl)-L-cysteinemethyl ester

The compound prepared in B above was reacted with N-CBZ-α-L-asparticacid-β-benzyl ester in a manner as previously described in Example 1D,to afford the above product.

D. α-L-aspartyl-S-(1-methylcyclohex-3-enyl)-L-cysteine methyl ester

The protected dipeptide from the previous step (277 mg, 0.54 mmol) wasdissolved in absolute ethyl alcohol (2 ml), and 10% palladium on carbon(240 mg) was added. The hydrogen source, 1,4-cyclohexadiene (1 ml, 10equiv.), was added, and ultrasound commenced for five minutes. Theslurry was then filtered through a bed of Celite with ethyl alcohol.Rotary evaporation afforded a white solid (1.58 mg).

EXAMPLE 16 A. N-CBZ-S-(1-(4-methylcyclohex-3-enyl)isopropyl)-L-cysteinemethyl ester

The ether is prepared from N-CBZ-L-cysteine methyl ester and α-limonenein a manner similar to that described in Example 1B. The product can becharacterized by NMR spectroscopy.

B. N-CBZ-B-benzylester-α-L-aspartyl-S-(1-(4-methylcyclohex-3-enyl)isopropyl)-L-cysteinemethyl ester

The amine olefin is prepared by transfer hydrogenation as described inExample 7B and coupled with N-CBZ-α-L-aspartic acid-β-benzyl ester bythe copper mediated procedure as described in Example 1D.

C. α-L-aspartyl-O-1-(4-(methylcyclohex-3-enyl)isopropyl)-L-cysteinemethyl ester

The protected dipeptide is deprotected by transfer hydrogenation, asdescribed in Example 7B to giveα-L-aspartyl-S-1-(4-methylcyclohex-3-enyl)isopropyl)-L-cysteine methylester.

D. α-L-aspartyl-S-(1-(cis-4-methylcyclohexyl)isopropyl)-L-cysteinemethyl ester

The product of B above is deprotected by catalytic hydrogenation in amanner as described in Example 1E to afford the above compound.

EXAMPLE 17 Preparation of DL-2-aminomalonyl-S-(1-methylcyclopentyl)-L-cysteine methyl ester A.N-CBZ-DL-2-amino malonic acid mono benzyl ester

Dibenzyl malonate (10.0 g, 35.2 mmol) was taken up in 1,4-dioxane (100mL) and treated with a 40% aqueous solution of acetic acid (35 mL),followed by the slow addition (2.5 h) of solid sodium nitrate (10 g).The reaction was stirred for another 2.5 h and extracted into ether(3×70 mL). The organic phase was washed with a 1% solution of NaHCO₃until the aqueous layer was slightly acidic (pH 5-6). The etherealsolution was dried over MgSO₄ and removed under reduced pressure to givean oil (10.9 g). The crude oxime was carried directly to the next step.

Amalgamated aluminum (obtained from 1.25 g, 0.463 g atom of aluminumfoil) was covered with tetrahydrofuran (28 mL) followed by 1.9 mL ofwater. The reaction mixture was stirred mechanically and cooled in a dryice acetone bath. A solution of the crude oxime (from the previous step)in 30 mL of tetrahydrofuran was added dropwise (20 min.) while thetemperature was maintained between -15° and -30° C. The ice bath wasremoved and spontaneous reaction occurred, which resulted in a rapidrise in temperature (50° C.). When the evolution of heat ceased, themixture was refluxed for 1 hour, diluted with ether (100 mL) andfiltered through Celite. The solvent was removed under reduced pressureto give the crude amine (7.5 g), which was taken to the following stepwithout further purification. The crude amine (7 g) was dissolved in asaturated solution of NaHCO₃ (200 mL) and cooled in an ice bath. Benzylchloroformate (4.0 g, 23 mmol) was added dropwise (0.5 h) to thevigorously stirred solution. The reaction mixture was left at roomtemperature for 12 hours, during which time the product precipitated.The product was collected by filtration, washed with water, dried inair, and recrystallized from i-PrOH: yield 4.8 g (52%) from dibenzylmalonate; m.p. 104°-106° C.

N-(benzyloxycarbonyl)-2-amino malonic acid dibenzyl ester (4.33 g, 10mmol) was dissolved in acetone/water (4.1, 133 mL). The solution wasstirred and lithium hydroxide monohydrate (0.42 g, 10 mmol) in water (11mL) was added dropwise (1 h). The reaction mixture was stirred for 12hours at room temperature, the acetone was removed under reducedpressure, and the residue was taken up into a saturated solution ofNaHCO₃ (60 mL) and extracted with EtOAc (3×100 ml). The EtOAc washingswere combined, dried over MgSO₄ and removed under reduced pressure togive a solid, which was crystallized from EtOAc/hexane. This solid wasidentified as recovered starting material (1.1 g, 25.4%). The aqueousphase was acidified with 3N HCl to pH=1 and extracted with CHCl₃ (4×50mL). The combined CHCl₃ washings were dried over MgSO₄ and the solventwas removed under reduced pressure to give a residue which crystallizedfrom i-PrOH: yield 2.0 g (58%); m.p. 114°-116° C.

B. N-CBZ-DL-2-amino malonyl benzylester-S-1-methylcyclopentyl)-L-cysteine methyl ester

The mono-carboxylic acid from the last step of Section A (2 g, 5.83mmol) was dissolved in dry acetonitrile (75 ml) at 0° C. under argon.Then, S-(1-methylcyclopentyl)-L-cysteine methyl ester (1.2 g, 1 equiv.)was added, as described in Example 1D. Lastly, dicyclohexylcarbodiimide(1.2 g, 1 equiv.) was added and the contents of the flasks were stirredat room temperature.

The reaction mixture was rotary evaporated to remove the acetonitrileand the residue was taken up in 0.1N hydrochloric acid (100 ml) andextracted with diethyl ether (3×100 ml). The ethereal layer was driedover sodium sulfate and filtered to remove insoluble urea. The ether isremoved by rotary evaporation. The coupled product was purified bysilica gel chromatography with 3:1 petroleum ether/ethyl acetate.

C. DL-2-amino malonyl-S-(1-methylcyclopentyl)-L-cysteine methyl ester

The bis-protected dipeptide from Section B was dissolved in absolutemethanol under argon. 10% Palladium on carbon was added andhydrogenation was carried out at 50 psi. After cessation of hydrogenuptake, the mixture was filtered through Celite and rotary evaporated togive a white solid.

EXAMPLE 18 L-Aspartyl-S-2,2,5,5-tetramethylcyclopentyl-L-cysteinemethylester A. L-N-Triphenylmethyl cysteine methyl ester

A solution of L-cysteine methyl ester hydrochloride (100 g), triphenylchloride (179.3 g) and triethylamine (197 ml) was stirred at 0° C. for 2hours, then allowed to warm to room temperature overnight. The solutionwas then washed successively with 10% aqueous citric acid and water,dried over magnesium sulfate, and the solvent was evaporated to yield212 g of the product (91% yield).

B. L-1-Triphenyl methyl aziridine-2-carboxylic acid methyl ester

A mixture of compound A (212 g), methanesulfonyl chloride (45.6 ml), andpyridine (1.76 l) was stirred at 0°, then allowed to warm slowly to roomtemperature overnight. Ethyl acetate (1.5 l) was added, and theresulting solution was washed with 10% aqueous citric acid and water,dried over magnesium sulfate and the solvent was removed. The residualoil was dissolved in tetrahydrofuran (2.5 l) and a triethylamine (143ml) was added. The mixture was heated at reflux overnight. The solutionwas then cooled, and most of the solvent was removed under vacuum. Theresidual oil was dissolved in ethyl acetate (2 l) and the solution waswashed succesively with 10% aqueous citric acid, saturated aqueoussodium bicarbonate, and water, was dried over magneisum sulfate, and thesolvent was evaporated under vacuum. The residue was dissolved in hotmethanol (300 ml). Upon cooling, compound B crystallized as an off-whitepowder which was removed by filtrtion and then air dried (115 g), (57%yield). The structure was confirmed by NMR. [α] _(D) =-90.5°±0.5 (C 1.0THF).

C. L-1-Benzyloxycarbonylaziridine-2-carboxylic acid methyl ester

To a cold solution (0°) of compound B (17.0 g) and methanol (100 ml) indichloromethane (100 ml) was added concentrated sulfuric acid (5.0 ml).The mixture was stirred at 0° for 10 min. Approximately half of thesolvent was removed under vaccum, and the residue was dissolved inether. This solution was extracted with water. The aqueous extract wasmade basic with sodium bicarbonate and extracted with dichloromethane(3×25 ml). To these combined extracts was added triethylamine (4.63 g)and the solution was cooled to 0°. Benzyl chloroformate (7.80 g), wasadded, and the mixture was allowed to warm to room temperatureovernight. The solution was then washed successively with 1M aqueoushydrochloric acid and saturated aqueous sodium bicarbonate, dried overmagnesium sulfate, and the solvent was removed under vacuum to yield abrown oil (7.0 g). The product was purified by column chromatography onsilica gel (4:1 hexanes: ethyl acetate, eluent) to yield compound C(3.44 g, 30%) as a slightly yellow oil. D.N-Benzyloxycarbonyl-S-2,2,5,5-tetramethylcyclopentyl-L-cysteine methylester

To a solution of compound C (1.00 g) and2,2,5,5-tetramethylcyclopentanol (1.2 g) in dichloromethane (20 ml) wasadded boron trifluoride diethyl ethereate (15 drops). The mixture wasstirred at room temperature for 4 hours, then washed with water, driedover magnesium sulfate and the solvent was evaporated. The residue waspurified by column chromatography (silica gel, 10:1, hexanes: ethylacetate, eluent) to yield compound D as a colorless oil (0.34 g, 21%yield).

E. S-2,2,5,5-Tetramethylcyclopentyl-L-cysteine methyl ester

Compound D (0.34 g) was deprotected by the usual procedure to yieldcompound E (0.214 g, 98% yield).

F. N-Benzyloxycarbonyl-α-L-aspartyl- β-benzylester-S-2,2,5,5-tetramethylcyclopentyl-L-cysteine methyl ester

Compound E (0.214 g) was coupled with N-benzyloxy carbonyl-L-asparticacid-β-benzyl ester (0.33 g) by the copper (II) chloride procedure toyield compound F (0.300 g, 60% yield).

G. α-L-Aspartyl-S-2,2,5,5-tetramethylcyclopentyl-L-cysteine methyl ester

Compound F (0.300 g) was deprotected by the usual procedure to yieldcompound G (0.090 g, 43% yield).

Using appropriate starting materials, the following compounds areprepared:

α-L-aspartyl-S-2,2,6,6-tetramethylcyclohexyl-L-cysteine methyl ester

α-L-aspartyl-S-1,2,7-trimethylcycloheptyl-L-cysteine methyl ester

α-L-aspartyl-S-1,2,2-trimethylcycloheptyl-L-cysteine methyl ester

α-L-aspartyl-S-2,2,7,7-tetramethylcycloheptyl-L-cysteine methyl ester

α-L-aspartyl-[S-(2,2,3,3-tetramethylcyclopropyl)]-L-cysteine methylester

α-L-aspartyl-[S-(2,2,4,4-tetramethylcyclobutyl)]-L-cysteine methyl ester

-L-aspartyl-[S-(2,2,5-trimethylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,5-dimethylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,2-dimethylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,2-dimethylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2,2,4,4-tetramethylcyclobutyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-methylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-methylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-isopropylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-isopropylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-t-butylcyclopentyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-t-butylcyclohexyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(dicyclopropylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(dicyclobutylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(t-butylcyclopropylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(t-butylcyclobutylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(fenchyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(benzyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(α-methylbenzyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(o-methylbenzyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-furylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(3-furylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-2-(5-methylfuryl)methyl]-L-cysteine methyl ester

α-L-aspartyl-[S-(2-thienylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-(3-thienylmethyl)]-L-cysteine methyl ester

α-L-aspartyl-[S-2-(5-methylthienyl)methyl]-L-cysteine methyl ester

EXAMPLE 19 α-L-Aspartyl-S-cyclopentyl-L-cysteine methyl ester

This compound is prepared according to the method as described inExample 18, except cyclopentanol is substituted for2,2,5,5-tetramethylcyclopentanol.

EXAMPLE 20 α-L-aspartyl-S-(1-methyl-cycloheptyl)-L-cysteine methyl esterand α-L-aspartyl-S-cyclopentyl-L-cysteine methyl ester

Using the same procedure as disclosed in Example 1 and substituting1-methyl-1-cycloheptene for methylene cyclopentane,α-L-aspartyl-S-(1-methylcycloheptyl)-L-cysteine methyl ester wasprepared.

Similarly, by using cyclopentene, α-L-aspartyl-S-cyclopentyl-L-cysteinemethyl ester was prepared.

EXAMPLE 21 A. N-CBZ-L-cysteine ethyl ester

Thionyl chloride (5.25 mL, 72 mmol, 3.6 equiv.) is added dropwise to a0° C. solution of absolute ethyl alcohol (20 ml). Diisopropyl ethylamine(3.45 ml, 19 mmol, 1 equiv.) was added as a solid. Stirring is continuedfor 16 hours at room temperature. The ethanol and thionyl chloride arethen removed by rotary evaporation and the residue is dissolved in ethylacetate (200 ml). The organic phase is washed with 1N hydrochloric acid(50 ml) and saturated sodium bicarbonate (50 ml) and brine (20 ml). Theproduct is dried with magnesium sulfate. Rotary evaporation of theproduct gave an oil which was chromatographed on silica gel withhexane/ethyl acetate (3:1) to give N-CBZ-L-cysteine ethyl ester.

The carbenzyloxy group was removed by the procedure as described inExample 1, C.

Using the above starting material, the ethyl esters of the compounds ofthe foregoing examples are prepared.

EXAMPLE 22 L-α-Aspartyl-O-(dicyclopropylmethyl)-L-serine methyl ester

This compound is prepared in accordance with the procedure of Example10, employing dicyclopropylmethanol as the alcohol starting material inlieu of 2,2,5,5-tetramethylcyclopentanol.

Similarly prepared from corresponding alcohols using this procedure are:

L-α-aspartyl-O-(cyclopropylcyclopentylmethyl)-L-serine methyl ester

L-α-aspartyl-O-(cyclopropyl-2-methylcyclohexylmethyl)-L-serine methylester

L-α-aspartyl-O-(cyclopentyl-2,5-dimethylcyclopentylmethyl)-L-serinemethyl ester

L-α-aspartyl-O-(cyclobutyl-2,2,6,6-tetramethylcyclohexylmethyl)-L-serinemethyl ester

L-α-aspartyl-O-(dicyclopentylmethyl)-L-serine methyl ester

L-α-aspartyl-O-(t-butylcyclopropylmethyl)-L-serine methyl ester

L-α-aspartyl-O-(t-butylcyclopentylmethyl)-L-serine methyl ester

EXAMPLE 23 L-α-Aspartyl-S-(dicyclopropylmethyl)-L-cysteine methyl ester

This compound is prepared in accordance with the procedure of Example10, employing dicyclopropylmethanol as the alcohol starting material inlieu of 2,2,5,5-tetramethylcyclopentanol.

Similarly prepared from corresponding alcohols using this procedure are:

L-α-aspartyl-S-(cyclopropylcyclopentylmethyl)-L-cysteine methyl ester

L-α-aspartyl-S-(cyclopropyl-2-methylcyclohexylmethyl)-L-cysteine methylester

L-α-aspartyl-S-(cyclopentyl-2,5-dimethylcyclopentylmethyl)-L-cysteinemethyl ester

L-α-aspartyl-S-(cyclobutyl-2,2,6,6-tetramethylcyclohexylmethyl)-L-cysteinemethyl ester

L-α-aspartyl-S-(dicyclopentylmethyl)-L-cysteine methyl ester

EXAMPLE 24 L-α-Aspartyl-O-phenyl-L-serine methyl ester

This compound is prepared in accordance with the procedure of Example10, employing phenol as the alcohol starting material in lieu of2,2,5,5-tetramethylcyclopentanol.

Similarly prepared from corresponding alcohols using this procedure are:

L-α-aspartyl-O-(2,6-dimethylphenyl)-L-serine methyl ester

L-α-aspartyl-O-(3,5-dimethylphenyl)-L-serine methyl ester

L-α-aspartyl-O-(2-methylphenyl)-L-serine methyl ester

L-α-aspartyl-O-benzyl-L-serine methyl ester

EXAMPLE 25 L-α-Aspartyl-S-phenyl-L-cysteine methyl ester

This compound is prepared in accordance with the procedure of Example10, employing phenol as the alcohol starting material in lieu of2,2,5,5-tetramethylcyclopentanol.

Similarly prepared from corresponding alcohols using this procedure are:

L-α-aspartyl-S-(2,6-dimethylphenyl)-L-cysteine methyl ester

L-α-aspartyl-S-(3,5-dimethylphenyl)-L-cysteine methyl ester

L-α-aspartyl-S-(2-methylphenyl)-L-cysteine methyl ester

EXAMPLE 26 Preparation of acid salts

The dipeptides described in the preceding examples are converted to acidsalts, e.g., hydrochlorides, by dissolving in an aqueous solutioncontaining an equivalent amount of acid, e.g., hydrochloric acid, andthe solution is evaporated to dryness to obtain the solid salt.Alternatively, alcoholic solutions of hydrogen chloride gas, e.g., HCl,dissolved in ethanol can be used in lieu of the aqueous acid solutionand the acid salt obtained by evaporation of solvent or crystallizationfrom the alcohol, e.g., by addition of a non-solvent.

Metal salts of the peptides of the preceding examples are prepared bydissolving an equivalent amount of the selected metal compound, e.g.,Na₂ CO₃, K₂ CO₃ or CaO, in water, dissolving the dipeptide in theresulting solution and evaporation of the resulting aqueous solution todryness.

EXAMPLE 27

The following cyclic ethers are prepared from the correspondingethylenically unsaturated compounds or the corresponding alcohol R₁ (CR₅R₆)_(n) OH using the respective procedures of the preceding examples.

    ______________________________________     ##STR9##    R.sub.1       n      R      R.sub.3                                     R.sub.5  R.sub.6    ______________________________________    pyranyl       0      Me     H    --       --    3-tetrahydrofuryl                  0      Me     H    --       --    3-tetrahydrofuryl                  1      Me     H    H        H    pyranyl       1      Me     H    cyclopropyl                                              H    2-methylfuryl 1      Me     H    H        H    2-methylfuryl 1      Me     H    cyclopropyl                                              H    3-(4,5-dihydrofuryl)                  1      Me     H    H        H    3-(4,5-dihydrofuryl)                  2      Me     H    H        H    3-(2,2,4,4-tetramethyl-                  0      Me     H    --       --    tetrahydrofuryl)    3-(2,2,4-trimethyl-                  0      Me     H    --       --    tetrahydrofuryl)    3-(2,4-dimethyl-                  0      Me     H    --       --    tetrahydrofuryl)    3-(2,2-dimethyl-                  0      Me     H    --       --    tetrahydrofuryl)    3-(4,4-dimethyl-                  0      Me     H    --       --    tetrahydrofuryl)    3-(2,2,4,4-tetra-                  0      Me     H    --       --    methyltetrahydro-    pyranyl)    4-(3,3,5,5-tetra-                  0      Me     H    --       --    methyltetrahydro-    pyranyl)    4-(3,3,5-trimethyl-                  0      Me     H    --       --    tetrahydropyranyl)    4-(3,5-dimethyl-                  0      Me     H    --       --    tetrahydropyranyl)    3-(2,2,4-trimethyl-                  0      Me     H    --       --    tetrahydropyranyl)    3-(2,2-dimethyl-                  0      Me     H    --       --    tetrahydropyranyl)    3-(4,4-dimethyl-                  0      Me     H    --       --    tetrahydropyranyl)    3-(2,4-dimethyl-                  0      Me     H    --       --    tetrahydropyranyl)    3-(tetrahydrothienyl)                  0      Me     H    --       --    3-(tetrahydrothienyl)                  1      Me     H    cyclopentyl                                              H    3-(tetrahydrothienyl)                  2      Me     H    cyclobutyl                                              H    3-(4,5-dihydrothienyl)                  1      Me     H    cyclopropyl                                              H    3-(2,2,4,4-tetramethyl-                  0      Me     H    --       --    tetrahydrothienyl)    3-(2,2,4-trimethyl-                  0      Me     H    --       --    tetrahydrothienyl)    3-(2,4-dimethyl-                  0      Me     H    --       --    tetrahydrothienyl)    3-(2,2-dimethyl-                  0      Me     H    --       --    tetrahydrothienyl)    3-furyl       1      Me     H    H        H    3-thienyl     1      Me     H    H        H    3-(2,4,4-trimethyl-                  0      Me     H    --       --    tetrahydrothienyl)    3-(2,2,4,4-tetramethyl-                  0      Me     H    --       --    1,1-dioxo-tetrahydro-    thienyl)    3-(2,2,4,4-tetramethyl-                  0      Me     H    --       --    1-oxo-tetrahydro-    thienyl)    3-(2,2,4-trimethyl-                  1      Me     H    cyclopentyl                                              H    1,1-dioxo-tetrahydro-    thienyl)    3-(2,4-dimethyl-1,1-                  0      Me     H    --       --    dioxo-tetrahydro-    thienyl)    3-(2,2-dimethyl-1,1-                  0      Me     H    --       --    dioxo-tetrahydro-    thienyl)    3-(4,4-dimethyl-1,1-                  0      Me     H    --       --    dioxo-tetrahydro-    thienyl)    3-(2,2,4-trimethyl-                  0      Me     H    --       --    1-oxo-tetrahydro-    thienyl)    5-methylfuryl 1      Me     H    H        H    5-methylthienyl                  1      Me     H    H        H    ______________________________________

EXAMPLE 28

A cherry flavored beverage is prepared by mixing 1.48 gms. of anunsweetened instant beverage base mix with 438 gms. of water and 0.025weight percent of L-aspartyl-S-(1-methylcyclopentyl)-L-cysteine methylester. The base contains a malic acid and monocalcium phosphate buffer,flavorants and colorants.

EXAMPLE 29

A vanilla flavored pudding is prepared by mixing 474 gms. of milk, 21.7gms. of an unsweetened pudding base mix and 0.036 weight percent ofL-aspartyl-S-(1-methyl-cyclohexyl)-L-cysteine methyl ester. The basecontains Na₂ HPO₄, tapioca starch emulsifiers, salt, flavorants andcolorants.

Representative compounds of this invention were tested for sweetnesswith the results being given in Table 1.

                  TABLE 1    ______________________________________     ##STR10##                  Concentra-          Sweetness                  tion of   Sucrose   ratio                  Compound  Equivalent                                      (Compound:    XR.sub.1      (%)       (%)       Sucrose)    ______________________________________    Ot-butyl.sup.a                  .05       6         120    O1-methylcyclopentyl                  .005      2.5       500                  .01       5         500                  .025      10        400    O1-methylcyclohexyl                  .005      2         400                  .01       4.5       450                  .025      8.5       340    O1-methylcyclobutyl                  .01       2         200                  .05       8         160    OCis-1,2-dimethyl-                  .005      2         400    cyclohexyl    .010      4         400                  .020      7         350    Otrans-1,2-dimethyl-                  .005      1.5       300    cyclohexyl    .010      3         300                  .020      5         250    O1-ethylcyclopentyl                  .005      2         400                  .01       4         400                  .02       6         300    O1-bornyl     .005      1         200                  .01       2.5       250                  .025      4.5       180    O1-methylcyclo-3-                  .005      2         400    hexenyl       .01       2.5       250                  .025      4         160    O2-(4-methylcyclo-                  .025      6         240    hexyl)isopropyl                  .05       11        220    O1-methylcycloheptyl                  .01       2         200                  .05       6         120    O[1,1-dimethyl-(4-                  .01       2.2       220    methylcyclohex-3-enyl)-                  .025      5.2       208    methyl]    O2-(4-norbornenyl)-                  .05       5.8       117    ethyl    O2-norbornylethyl                  .04       4.2       105    O2,2,5,5-tetramethyl-                  .0225     3         1200    cyclopentyl   .005      5         1000                  .01       8         800    Ocyclopentyl  .005      1.5       300                  .01       2.3       230                  .025      4.5       180    Ocyclohexyl   .01       1.2       120                  .025      3.2       128    O2-cis-cyclohexyl                  .005      1.8       360                  .01       3.2       320                  .025      6         240    O2,2-dimethylcyclo-                  .005      3         600    pentyl        .01       5.3       530                  .025      9         360    Otrans-2-methylcyclo-                  .01       3         300    pentyl        .025      5.3       212    S1-methylcyclopentyl                  .0025     5         2000                  .005      6         1600    ______________________________________     .sup.a previously known compound

In comparison with sweetness values observed with present new compounds,the corresponding alkyl ethers of L-aspartyl-L-serine methyl estersdemonstrate a lower order of sweetness. Table 2 summarizes the sweetnessvalues for representative alkyl ethers, as reported in the prior art.

                  TABLE 2    ______________________________________     ##STR11##    R.sub.1       X       Sucrose Equivalent    ______________________________________    tert. C.sub.4 H.sub.9                  O       140.sup.a    tert. C.sub.5 H.sub.11                  O       230.sup.b    methyl        S        1.sup.a    ethyl         S        40.sup.a    propyl        S       130.sup.a    isopropyl     S       170.sup.a    t-butyl       S       900.sup.a    methyl        CH.sub.2 S                           80.sup.a    ______________________________________     .sup.a Van der Heijden, Brusse and Peer, Chemical Senses and Flavour, 4,     141-152 (1979).     .sup.b U.S. Pat. No. 3,798,204.

What is claimed is:
 1. A compound represented by the formula: ##STR12##wherein R is alkyl containing 1-3 carbon atoms;when X=S R₁ iscycloalkyl, cycloalkenyl, lower alkyl-substituted cycloalkyl orcycloalkenyl, bicycloalkyl, bycycloalkenyl, tricycloalkyl, aryl,alkylaryl, cyclic ether, cyclic thioether, cyclic sulfoxide or cyclicsulfone, containing up to 10 ring carbon atoms and up to a total of 12carbon atoms; when X=O R₁ is cyclic ether or cyclic thioether containingup to 10 ring carbon atoms and up to a total of 12 carbon atoms; R₂, R₃,R₄ and R₆ are each H or lower alkyl; R₅ is H, lower alkyl or cycloalkylcontaining up to 3-5 ring carbon atoms; each n=0, 1 or 2; m=0 or 1; Z isan alkylene chain containing 0-2 carbon atoms in the principal chain andup to a total of 6 carbon atoms; and food acceptable salts.
 2. Thecompound according to claim 1 wherein R¹ is cyclopentyl or cyclohexylcontaining a total of up to 10 carbon atoms.
 3. The compound accordingto claim 2 wherein each n=0 and R₃ and R₄ are each H.
 4. A compoundrepresented by the formula: ##STR13## wherein X=SR is alkyl containing1-3 carbon atoms; R₁ is cycloalkyl, cycloalkenyl, loweralkyl-substituted cycloalkyl or cycloalkenyl, bicycloalkyl,bicycloalkenyl, tricycloalkyl, aryl, alkylaryl, cyclic ether, cyclicthioether, cyclic sulfoxide or cyclic sulfone, containing up to 10 ringcarbon atoms and up to a total of 12 carbon atoms; R₂, R₃, R₄ and R₆ areeach H or lower alkyl; R₅ is H, lower alkyl or cyloalkyl containing upto 3-5 ring carbon atoms; each n=0, 1 or 2; m=0 or 1; Z is an alkylenechain containing 0-2 carbon atoms in the principal chain and up to atotal of 6 carbon atoms; and food-acceptable salts.
 5. The compoundaccording to claim 4 whereinR₁ is cyclopentyl or cyclohexyl containing atotal of up to 10 carbon atoms.
 6. The compound according to claim 4wherein each n=0 and R₃ and R₄ are each H.
 7. A compound represented bythe formula: ##STR14## wherein X=S;R is alkyl containing 1-3 carbonatoms; R₁ is cycloalkyl, cycloalkenyl, lower alkyl-substitutedcycloalkyl or cycloalkenyl, bicycloalkyl, bicycloalkenyl, tricycloalkyl,aryl, alkylaryl, cyclic ether, cyclic thioether, cyclic sulfoxide orcyclic sulfone, containing up to 10 ring carbon atoms and up to a totalof carbon atoms; R₃, R₄ and R₆ are each H or lower alkyl; R₅ is H, loweralkyl or cyloalkyl containing up to 3-5 ring carbon atoms; each n=0, 1or 2; m=0 or 1; Z is an alkylene chain containing 0-2 carbon atoms inthe principal chain and up to a total of 6 carbon atoms; andfood-acceptable salts.
 8. The compound according to claim 7 wherein R₁is cyclopentyl or cyclohexyl containing a total of up to 10 carbonatoms.
 9. The compound according to claim 7 wherein n=0 and R₃ and R₄are each H.
 10. A compound represented by the formula: ##STR15## whereinX=S;R₁ is cycloalkyl, cycloalkenyl, lower-alkyl-substituted cycloalkylor cycloalkenyl, bicycloalkyl, bicycloalkenyl, tricycloalkyl, aryl,alkylaryl, cyclic ether, cyclic thioether, cyclic sulfoxide or cyclicsulfone, containing up to 10 ring carbon atoms and up to a total of 12carbon atoms; R₃ is H or lower alkyl; and food-acceptable salts.
 11. Thecompound according to claim 10 wherein R₁ is cyclopentyl or cyclohexylcontaining a total of up to 10 carbon atoms.
 12. A compound representedby the formula: ##STR16## wherein X=S;R₁ is cyclolakyl, cycloalkenyl,lower alkyl-substituted cycloalkyl or cycloalkenyl, bicycloalkyl,bicycloalkenyl, tricycloalkyl, aryl, alkylaryl, cyclic ether, cyclicthioether, cyclic sulfoxide or cyclic sulfone, containing up to 10 ringcarbon atoms and up to a total of 12 carbon atoms; R₅ is H, lower alkylor cycloalkyl containing up to 3-5 ring carbon atoms; n=0 or 1; and foodacceptable salts.
 13. The compound according to claim 12 wherein R₁ iscyclopentyl or cyclohexyl containing a total of up to 12 carbon atoms.14. The compound according to claim 12 wherein R₁ is cyclopentyl orcyclohexyl containing a total of up to 10 carbon atoms.
 15. A compoundrepresented by the formula: ##STR17## wherein R₁ is cycloalkyl,cycloalkenyl, lower alkyl-substituted cycloalkyl or cycloalkenyl,bicycloalkyl, tricycloalkyl, benzyl, aryl or alkylaryl, cyclic ether orthioether, containing up to 10 ring carbon atoms and up to a total of 12carbon atoms;and food acceptable salts.
 16. The compound according toclaim 15 wherein R₁ is cyclopentyl or cyclohexyl containing a total ofup to 12 carbon atoms.
 17. The compound according to claim 15 wherein R₁is cyclopentyl or cyclohexyl containing a total of up to 10 carbonatoms.
 18. A compound of the formula: ##STR18## wherein X=S;R is alkylcontaining 1-3 carbon atoms; R₁ is a mono-, di-, tri or tetra(loweralkyl)cycloalkyl containing up to 7 ring carbon atoms, and a total of upto 12 carbon atoms; R₂, R₃, R₄ and R₆ are each H or lower alkyl; R₅ isH, lower alkyl or cycloalkyl containing 3-5 ring carbon atoms; each n=0,1 or 2; Z is an alkylene chain containing 0-2 carbon atoms in theprincipal chain and up to a total of 6 carbon atoms; and food-acceptablesalts.
 19. The compound according to claim 18 wherein R₁ is abeta-alkyl-substituted cycloalkyl group wherein the alkyl group contains1-5 carbon atoms.
 20. A compound according to claim 18 wherein R₁ isβ-methyl-substituted cycloalkyl.
 21. A compound according to claim 18wherein R₁ is a β,β'-dimethyl-substituted cycloalkyl.
 22. A compoundaccording to claim 18 wherein R₁ is β,β-dimethyl substituted cycloalkyl.23. A compound according to claim 18 wherein R₁ is a β,β,β'-trimethylsubstituted cycloalkyl.
 24. A compound according to claim 18 wherein R₁is β,β,β',β'-tetramethyl substituted cycloalkyl.
 25. A compound of theformula: ##STR19## wherein X=S;R₁ is a mono-, di-, tri-, ortetramethylcycloalkyl containing up to 7 ring carbon atoms; R₃ is H orlower alkyl; and food acceptable salts.
 26. The compound according toclaim 25 wherein R₁ is a beta-alkyl substituted cycloalkyl group whereinthe alkyl group contains 1-5 carbon atoms.
 27. A compound according toclaim 25 wherein R₁ is a β-methyl-substituted cycloalkyl.
 28. A compoundaccording to claim 25 wherein R₁ is a β,β'-methyl-substitutedcycloalkyl.
 29. A compound according to claim 25 wherein R₁ is aβ,β-dimethyl-substituted cycloalkyl.
 30. A compound according to claim25 wherein R₁ is a β,β,β'-trimethyl-substituted cycloalkyl.
 31. Acompound according to claim 25 wherein R₁ is aβ,β,β',β'-tetramethyl-substituted cycloalkyl.
 32. A compound of theformula: ##STR20## wherein R₁ is a mono-, di-, tri-, ortetramethylcycloalkyl containing up to 7 ring carbon atoms;and foodacceptable salts.
 33. The compound according to claim 32 wherein R₁ is abeta-alkyl substituted cycloalkyl group wherein the alkyl group contains1-5 carbon atoms.
 34. A compound according to claim 32 wherein whereinR₁ is β-methyl-substituted cycloalkyl.
 35. A compound according to claim32 wherein R₁ is β,β-dimethyl-substituted cycloalkyl.
 36. A compoundaccording to claim 32 wherein R₁ is β,β-dimethyl-substituted cycloalkyl.37. A compound according to claim 32 wherein R₁ isβ,β,β'-trimethyl-substituted cycloalkyl.
 38. A compound according toclaim 32 wherein R₁ is β,β,β',β'-tetramethyl-substituted cycloalkyl. 39.A compound represented by the formula: ##STR21## wherein X=S;R is alkylcontaining 1-3 carbon atoms; R₁ is cyclic ether, thioether, sulfoxidesor sulfones containing 4-5 ring carbon atoms and up to a total of 10carbon atoms; R₂, R₃ and R₆ are each H or lower alkyl; R₅ is H, loweralkyl or cycloalkyl containing up to 3-5 carbon ring atoms; each n=0, 1or 2; m=0 or 1; Z is an alkylene chain containing 0-2 carbon atoms inthe principal chain and up to a total of 6 carbon atoms; and foodacceptable salts.
 40. α-L-Aspartyl-O-dicyclopropylmethyl cysteine methylester.
 41. α-L-Aspartyl-S-(1-methylcyclopentyl)-L-cysteine methyl ester.42. α-L-Aspartyl-S-(1-methylcyclohexyl)-L-cysteine methyl ester. 43.α-L-Aspartyl-S-(1-methycyclobutyl)-L-cysteine methyl ester. 44.α-L-Aspartyl-S-(cis-1,2-dimethylcyclohexyl)-L-cysteine methyl ester. 45.α-L-Aspartyl-S-(trans-1,2-dimethylcyclohexyl)-L-cysteine methyl ester.46. α-L-Aspartyl-S-(1-ethylcyclopentyl)-L-cysteine methyl ester. 47.α-L-Aspartyl-S-(1-methylcyclopentyl)-L-cysteine ethyl ester. 48.α-L-Aspartyl-S-(1-methylcyclohex-3-enyl)-L-cysteine methyl ester. 49.α-L-Aspartyl-S-(2-(4-methylcyclohexyl)-propyl)-L-cysteine methyl ester.50. α-L-Aspartyl-S-(1-ethylcyclopentyl)-L-cysteine methyl ester. 51.α-L-Aspartyl-S-([1-(6,7,7-trimethylnorbonyl)]-L-cysteine methyl ester.52. α-L-Aspartyl-S-([2-(4-methylcyclohexyl)isopropyl]-L-cysteine methylester.
 53. α-L-Aspartyl-S-(2,2,5,5-tetramethylcyclopentyl)-L-cysteinemethyl ester. 54.α-L-Aspartyl-S-(2,2,6,6-tetramethylcyclohexyl)-L-cysteine methyl ester.55. α-L-Aspartyl-S-(2,2-dimethylcyclopentyl)-L-cysteine methyl ester.56. α-L-Aspartyl-S-(2,2,5-trimethylcyclopentyl)-L-cysteine methyl ester.57. α-L-Aspartyl-S-(2,2,6-trimethylcyclohexyl)-L-cysteine methyl ester.58. α-L-Aspartyl-S-(dicyclopropylmethyl)-L-cysteine methyl ester. 59.α-L-Aspartyl-S-(t-butylcyclopropylmethyl)-L-cysteine methyl ester. 60.α-L-Aspartyl-S-(2-isopropylcyclopentyl)-L-cysteine methyl ester. 61.α-L-Aspartyl-S-(2-t-butylcyclopentyl)-L-cysteine methyl ester. 62.α-L-Aspartyl-S-(2-isopropylcyclohexyl)-L-cysteine methyl ester. 63.α-L-Aspartyl-S-(2-t-butylcyclohexyl)-L-cysteine methyl ester. 64.α-L-Aspartyl-S-(2,2,4,4-tetramethylbutylcyclobutyl)-L-cysteine methylester.
 65. α-L-Aspartyl-S-2-(2-methylcyclohex-3-enyl)propyl-L-cysteinemethyl ester.
 66. α-L-Aspartyl-S-l-(norbornenyl)ethyl-L-cysteine methylester.
 67. α-L-Aspartyl-S-l-(l-norbornyl)ethyl-L-cysteine methyl ester.68. α-L-Aspartyl-S-(cyclopentyl)-L-cysteine methyl ester. 69.α-L-Aspartyl-S-(cyclohexyl)-L-cysteine methyl ester. 70.α-L-Aspartyl-S-(fenchyl)-L-cysteine methyl ester.
 71. A compoundrepresented by the formula: ##STR22## wherein R is alkyl containing 1-3carbon atomsR₁ is cyclic ether or cyclic thio-ether containing up to 10ring carbon atoms and up to 12 carbon atoms; R₂ and R₄ are each H alkylcontaining 1-3 carbon atoms; R₃ is H, alkyl containing 1-6 carbon atomsor cycloalkyl containing 3-5 ring carbon atoms; n=0, 1 or 2; and m=0 or1; and food acceptable salts thereof.
 72. A compound according to claim71 wherein R₁ is tetrahydrofuryl or tetrahydrothienyl.
 73. A compoundaccording to claim 71 wherein R₁ is β-methyl substituted cyclic ether orcyclic thioether.
 74. A compound according to claim 71 wherein R₁ isβ,β-dimethyl substituted cyclic ether or cyclic thioether.
 75. Acompound according to claim 71 wherein R₁ is a β,ββ'-trimethylsubstituted cyclic ether or cyclic thioether.
 76. A compound accordingto claim 71 wherein R₁ is a β,β,β',β',-tetramethyl substituted cyclicether or cyclic thioether.
 77. A compound according to claim 71 which isα-L-Aspartyl-[O-(3-tetrahydrothienyl)]-L-serine methyl ester.
 78. Acompound according to claim 71 which isα-L-Aspartyl-[0-3-(2,2,4,4-tetrahmethyltetrahydrothienyl)]-L-serinemethyl ester.
 79. A compound according to claim 71 which isα-L-Asparatyl-[0-3-(2,2,4-trimethyltetrahydrothienyl)]-L-serine methylester.
 80. A compound according to claim 71 which isα-L-Aspartyl-[3-(2,4-dimethyltetrahydrothienyl)]-L-serine methyl ester.81. A compund according to claim 71 which isα-L-Aspartyl-[3-(2,2-dimethyltetrahydrothienyl)]-L-serine methyl ester.82. A compound according to claim 71 which isα-L-Aspartyl-[3-(2,4,4-trimethyletetrahydrothienyl)]-L-serine methylester.